The Editor/Assembler module

The Editor/Assembler module is a pure GROM cartridge. It contains only one GROM, with addresses >6000-7800. It answers to any GROM base (>9800 to >983C).

Strangely enough, the GROM does not contain an editor, nor an assembler: these are assembly language programs provided on a companion disk. All the cartridge does is to display nice menus that let you load these programs (or others of your choice). On the plus side, the cartridge contains a linking-loader that can process the tagged-object files produced by the assembler and several subroutines to be called from TI-Basic.

If you wish, you can view a commented disassembly of that GROM in three parts: main program, subprograms, assembly routines.

Main menu
Editor menu
Assembler menu
Load-and-run menu
Run menu
Run-program-file menu


Programming tricks
Forced loading
Preventing "undefined" symbol errors
Using the illegal tags
Biased loading
Extra assembler opcodes

File formats
EA5 (program file)
Tagged object code (DF80 file)


The GROM contains only one GPL program: EDITOR/ASSEMBLER, whose start point is >6025 in GROM memory.


When entered, the program loads the built-in character sets from the console GROM:

  • small upper-case chars 32-95 at VDP address >0900-0AFF,
  • lower-case characters 96-127 at VPD address >0B00-0BF7,
  • empty chars 0-31 at VDP address >0800-08FF, except for:
  • copyright character (10) at address >0850-0857,
  • editor cursor (a solid 8x3 pixels vertical bar) at address >08F0-08F7 (i.e. char 30),
  • module cursor (an empty 6x6 square) at address >08F8-08FF (i.e. char 31).
  • For some reason, provision is made to load a different set of characters, possibly corresponding to another console version: the distinction is made by scanning the keyboard with keyboard type 5. If the type is not changed to 0 by the scanning routine, characters >32-95 will be loaded at addresses >0A00-0BFF in VDP memory, then characters 64-95 are modified by adding a small 2-pixel dash in their upper left corner. I have no idea what this is meant for, the TI-99/4 may be?

    The VDP registers are then set with the following values:

    R1=E0 Standard mode
    R2=00 Screen image at >0000
    R3=0E Color table at >0380
    R4=01 Char pattern table at >0800
    R5=06 Sprite attribute table at >0300
    R6=00 Sprite pattern table at >0000 (not the same as char pats!)
    R7=F5 White on blue

    Main menu


    1 TO EDIT
    4 RUN


    Option 1 enters the editor menu.
    Option 2 calls the assembler.
    Option 3 is used to load an assembly file in tagged-object code, it enters option 4 when done.
    Option 4 is used to run a program loaded in memory with option 3.
    Option 5 is used to load and run a memory-image file, in "program" format.
    Fctn-9 resets the TI-99/4A.

    The editor menu

     * EDITOR *

    1 TO LOAD
    2 EDIT
    3 SAVE
    4 PRINT
    5 PURGE

    Option 1 causes the editor to load a DV80 or a DF80 file in memory.
    Option 2 enters the editor with the file currently in memory (if any).
    Option 3 causes the editor to save the file currently in memory.
    Option 4 prints a file.
    Option 5 purges the file currently in memory (so that option 2 can be used to edit an empty document).
    Fctn-9 returns to the main menu.

    Options 1 to 3 first check whether the editor is already in memory. This is done by looking for a flag value of >55AA in word >2000. If the editor isn't in memory, it is loaded from a "program" file called "EDIT1". This file must be in the standard "Option 5" format, which means that loading could continue with EDIT2 (it won't). The program then automatically performs the equivalent of option 5 (i.e. clears 3 words at >FFD8).

    Option 1 prompts the user for a file name and prepares a PAB for that file in VDP memory at address >1000 (pointed at by word >831C). The data buffer for that PAB will be located at >1080. The program then calls subroutine >0010 in GROM memory to attempt opening the file as a Div/Fix 80 file (the format of object files). If it fails, the program changes the file type to Div/Var 80 (the format of source files) and tries again. If it fails again an I/O error is announced, otherwise the editor is entered via an XML >21 (i.e. vector in >2002).

    Option 2 enters the editor via an XML >23 (i.e. vector in >2006). Upon return, VDP register 1 is put in standard mode again, the GPL Cnd bit in >837C in checked. If it is set, the program displays an error message whose number is taken from byte >8322, otherwise it just returns to the editor menu.

    Option 3 displays "VAR 80 FORMAT(Y/N)?" to know whether the file should be saved as a source file in DV80 format, or as an object file in DF80 format. Then it prompts the user for a filename and creates the PAB, just like option 1. Finally it calls the editor via an XML >22 (i.e. vector in >2004).

    Option 4 prompts the user for a filename just as options 1 and 3. Then it asks for a printer name. If the name is "TP" (Texas Instruments thermal printer) the default record length is set as 32 chars, but the printer is given a chance to modify this value. For all other printers, the record length is set as 80 chars. The program creates a PAB for the printer in at address >1100 in VDP memory. Records are then read from the file and written to the printer until an I/O error #5 occurs (i.e. "past eof"). The error is not announced though: instead both PABs are closed and the programs returned to the editor menu.

    A special processing occurs for the thermal printer: all trailing spaces are removed, and char 12 (form feed) is replaced with four spaces. Then the 80-byte long file records are split in chunks corresponding to the record length of the printer.

    Option 5 displays "ARE YOU SURE(Y/N)?" If the user presses "Y" the routine clears three words in the high-mmemory expansion: >FFD8-FFDD.

    The assembler menu

      * ASSEMBLER * 

    user input
    user input
    optional user input
    optional user input

    The module first checks whether the assembler is already in memory. This is signaled by a flag value of >AA55 in word >2000. If this is not the case, the programs displays "LOAD ASSEMBLER(Y/N)?", the user can answer "N" to avoid overwritting a program in memory, in case the assembler menu was entered by mistake (in the Editor menu, you must press two keys before anything is loaded, therefore no confirmation is required). If the user elects to load the assembler, the module loads it as a "program" file in EA5 format, named ASSM1, loads it and proceeds with a file named ASSM2. It then uses the GPL routine >0010 to call subroutine >16 in the disk controller (this is the assembly equivalent of a CALL FILES) and sets the number of available files to four.

    At this point, the user is successively prompted for:

    Finally, the sceen is cleared and the assembler is called via an XML >21 (i.e. vector in >2002). Upon return, the Cnd bit in the GPL status byte is checked for a possible error (whose number will be in >8322), otherwise the files are closed, and the message "PRESS ENTER TO CONTINUE" is displayed at the bottom of the screen. This allows the user to read any messages issued by the assembler (generally syntax errors...). Once the user presses <enter> the program returns to the main menu. However, the assembler is still in memory and won't be reloaded if the user enters the assembler menu again.

    The load-and-run menu

      * LOAD AND RUN *           

    user input (multiple)
    user input

    This option prompts the user for a file name and creates a PAB for it at address >1000 in VDP memory. It then checks whether a memory expansion is installed (by writing test values at >2000 and reading them back) and issues an error message if this is not the case. Otherwise, the program downloads assembly language routines stored in GROM at >7000-7730 into the low memory expansion at addresses >2000-2007, >2022-2676 and >3F38-3FFF. One of the routines is the linking-loader itself. The area above >3F38 is the beginning of the symbol table used by the loader (growing downwards) and contains pre-defined values.

    The loader is then called via an XML >22 (i.e. vector in >2004, just loaded above). The loader can return with an error by setting the Cnd bit in the GPL status byte and placing the error code in byte >8322. The module will then issue an error message and (in most cases) re-enter the load-and-run menu.

    If all went OK, the user is prompted for another filename, just as above. Note that the program sets a flag bit in byte >8349 so that the assembly routines won't be loaded again. The loader is then called again and the whole process repeats until the user enters an empty filename.

    At this point, the module looks for a flag value of >A55A in word >2000 (indicating that the assembly routines were loaded). If the correct value is not found the assembly routines will be loaded as above. In any case, it the branches to the "RUN" menu.

    The run menu

      * RUN *                 

    user input

    This menu can either be entered from the main menu, which displays the " * RUN * " title, or from the "load-and-run" menu, after the user entered an empty filename.

    The user is prompted for a 6-character program name. This must correspond to an assembly label, i.e. contain only upper-case letters and digits, the first character cannot be a digit. This label should be present in the symbol table, either because it's part of the pre-defined table or because it was placed here by the loaded (as a result of an assembly-language DEF statement).

    The module checks for a flag value of >A55A in word >2000, indicating that the standard assembly language routines were dumped from the GROM. If the value is not found, a "PROGRAM NOT FOUND" error is issued.

    Then the module sets up the VDP for the program to be executed: the color table is filled with >13 bytes (black on light green), the screen is erased, and VDP register 7 is set as >F3 (white on light green). Finally, the linker is entered via an XML >21 (i.e. vector in >2002). Upon return, the Cnd bit in the GPL status byte will cause an error message, if it's set. The error code is taken from byte >8322, that was cleared before calling the linker. Otherwise, the VDP setup of the module is restored, and the message ""PRESS ENTER TO CONTINUE" is displayed at the bottom of the screen.

    When the user presses <enter> the program returns to the main menu. Note however that nothing is erased in memory, so the user can select option 4 again and run another program, or the same one. To run the same program again, the user can just enter an empty program name.

    The program menu


    user input (optional)

    The user is prompted for an optional file name. This must be an existing "program" file containing a memory dump with a six-byte header (a format sometimes known as EA5, for Editor/Assembler option 5). If the user enters an empty string, the filename "UTIL1" will be used. A PAB for the file is prepared at VDP address >1000, with a data buffer area at >1380 and a maximum lenght of >2100 bytes.

    If the filename begins with "CS" the screen will be cleared to allow for proper display of the cassette management prompts. Then the program then displays "ONE MOMENT PLEASE..." at the bottom of the screen and calls the DSR that will load the file in VDP memory. It then transfers the file in CPU memory, according to the instructions of the 6-byte header. If the header calls for additional files, the last character of the filename in incremented by 1 (i.e. UTIL1 becomes UTIL2, etc), and the process starts again.

    Otherwise, the module sets up the VDP for the program to be executed: the color table is filled with >13 bytes (black on light green), the screen is erased, and VDP register 7 is set as >F3 (white on light green). Finally, the program is entered at the address where the first file was loaded, using an XML >F0 (i.e. vector in >8300).

    Upon return (note that many third-party programs do not return, they just reset the TI-99/4A), the VDP setup of the module is restored, and the Cnd bit is tested in the GPL status byte >837C. If it is set, an error code taken from byte >8322 is displayed in hexadecimal. In any case, the module displays "PRESS ENTER TO CONTINUE" at the bottom of the screen, and waits for the user to react. It then returns to the main menu.

    Note that it is not possible to re-enter the user program without reloading it.

    Creating EA5 memory-image files

    No provision is made in the cartridge to produce EA5 files. However, the accompanying disk comes with a small utility called SAVE. This utility REFerences three labels that should be DEFined by the program to save: SFIRST is the first address to save, SLAST is the last address to save, and SLOAD is where the program should be loaded by option 5 (generally, SLOAD is identical to SFIRST, but this is not an absolute requirement). Load your program first with option 3, then load SAVE: it will autostart upon loading and automatically save the program on a "program" file called DSK1.UTIL1

    You can do the same (and more) with my MISS utility, downloadable from this website. Or you could use R.A. Green's RAG linker produce a memory-image EA5 file directly from the tagged-object DF80 files.



    All this subprogram does is to load the assembly language subroutines stored in GROM at >7000-7730 into the low memory expansion at addresses >2000-2007, >2022-2676 and >3F38-3FFF. It therefore empties the symbol table and re-initializes the loading pointers.


    This subprogram can actually perform two distincts functions: place numeric values at a given address in cpu memory, or call the loader and load a tagged-object file into memory. Which function is selected depends on the type of parameter passed to the subprogram: a (non-empty) string constant or string variable calls the loader, a number or a numeric variable patches the memory.

    When a filename is passed as an argument, e.g. CALL LOAD("DSK1.MYFILE"), the subprogram loads the standard assembly language routines then calls the loader with XML >22. Upon return, if the Cnd bit of the status byte is set, an error will be returned. Otherwise, LOAD resumes parsing the parameters. This means you can load several files, or mix file loading and memory patching (however, once you started memory patching, you cannot load any more files).

    To load values into memory, you must first specify the destination address as a number from -32768 to +32767, where nagetive numbers correspond to addresses in the range >8000-FFFF. LOAD calls XML >12 to convert the real number into an integer. The following parameters must contain the bytes to place in memory, therefore the useful range is 0-255. Note that you can specify any value from -32768 to 32767, but only the least significant byte of the integer will be loaded.

    If you want to specify a new address in the same CALL LOAD statement, you can use an empty string constant (or variable) as a separator. The string must be empty so that it is not mistaken for a filename: non-empty strings issue a "bad argument" error.


    CALL LOAD("DSK1.MYFILE","DSK2.HISFILE",-24576,65,66,"",-20480,0,218,)

    Loads a tagged-object code file called MYFILE into memory,
    loads the file HISFILE into memory,
    places bytes 65 and 66 (i.e. "AB") at location >A000,
    and places bytes 0 and 218 at location >B000.


    Works exactly like LOAD, except that the target is the VDP memory. The address should therefore be in the range 0-3FFF (i.e. 16383). Of course, as programs can't run in VDP memory, it is not allowed to pass a filename within a CALL POKEV.


    This subprogram performs the opposite of LOAD: it fetches bytes from VDP memory and transfers them in numeric variables.

    Just like LOAD, you must specify an address in the range -32768 to +32768 either as a number or as a numeric variable. Then you can enter as many numeric variables as you like: each will receive one byte corresponding to the content of the cpu memory, starting at the specified address. Values will be in the range 0-255.

    You can use an empty string as a separator to enter a new address, but non-empty strings will cause an error.


    CALL PEEK (12,CLOCK,"",72,A,B,C,D)

    Gets the content of byte >000C into the variable CLOCK (this is the console clock frequency: 48 for 3 MHz or 40 for 2 MHz).

    Then gets the vectors for extended operation 2 (which does not exist in all consoles). The next two statements combine the bytes into words: XOP2WR should be 33696 (i.e.>83A0) and XOP2PC should be 33536 (>8300).


    Does the same as PEEK, but gets values from the VDP memory. Addresses should therefore be in the range 0-16383 (i.e >3FFF).


    This subprogram is used to begin execution of a program loaded with CALL LOAD. The first argument should be a quoted string, or a string variable containing the program name (i.e. an assembly DEFined label).

    Optionally, you can specify upto 16 additional parameters that will be passed to the executed programs. LINK fetches each parameter from the Basic symbol table, concatenates & strings if necessary, and places a numeric value or a string pointer on the value stack in VDP memory. These values can be retrieved be the called program via XML >18.

    In addition, LINK places the total number of variables in byte >8212 and indicates the type of variable (number, string constant, numeric variable, etc) into bytes >200A-2019, one byte per parameter. Note that this is different from CALL LINK in Extended Basic, that places the parameter types at >8300.

    The parameter type values can be:
    0: number
    1: quoted string
    2: numeric variable
    3: string variable
    4: numeric array element
    5: string array element

    All this makes parameter handling much easier for programs called from Basic. It's not really a piece of cake though...

    Once all parameters have been processed, LINK calls the linker via XML >21, with the program name in >834A-834F and the name length in word >8350-8351. If the name was en empty string, the linker will attempt to call again the previously executed program, if any.

    Upon return, ar error is issued if the Cnd bit is set in the GPL status byte. The error number is taken from byte >8322. If no error occured the subprogram removes all parameters from the value stack, if that wasn't done by the called program, and checks that the Basic statement terminates correctly (i.e >8342 must contain >00). Then it returns to Basic.


    This subprogram is used to retrieve the pattern of a character, in the range 32-159.

    The first parameter must be a number or a numeric variable: this is the number of the character of interest. The second parameter must be a string variable. Upon return, it will contain an hexadecimal description of the pattern, just like the ones used by the Basic CALL CHAR.



    A$ now contains the pattern for character 97, the lower case A: "00000038447C4444"

    Programming tricks

    And now, a few receipes on how to push that module a little further. Mostly, they deal with the loader that is part of the Editor/Assembler cartridge. There is no guaranty that these trick will work with a different loader...

    Forcing loading at a given address

    Normally, any code that was assembled as relocatable (RORG sections) can be loaded anywhere in memory. That's the whole purpose of the tagged-object file format. The cartridge's loader decides where to load a given file according to the following algorithm:

    To achieve this task, the loader maintains four pointers in the low memory expansion, at a location pointed at by label UTLTAB (normally >2022).

    Address Initially Usage                                 
    >2022 >0000 Previous program address
    >2024 >A000 First free address in high memory: FSTHI
    >2026 >FFD7 Last free address in high memory: LSTHI
    >2028 >2676 First free address in low memory: FSTLOW
    >202A >3F38 Last free address in low memory (bottom of symbol table): LSTLOW
    >20DA-20F9 Linking-loader worskpace.

    Each time it loads a file in the high memory expansion, the loader updates the value of FSTHI. Similarly, it updates FSTLOW when loading a file in the low memory expansion, and LSTLOW when adding labels to the symbol table (or removing labels, when a REF is solved by an incoming DEF).

    Now there may be times when we want to force loading of a relocatable file at a given address in memory. We could reassembled it, using an AORG statement that will force loading at a given address. But this is not very convenient, especially if we don't have the source for that file. A better alternative is to write a tiny file that will fool the loader by altering the loading pointers with AORG statements. For instance, the following file forces loading of the next relocatable file at >C000 in high memory.

    * This program forces the loader to load relocatables files starting at >C000
    * Load it before just before the reloc file
    AORG >2024
    DATA >C000 You can put any value here

    To force loading in the low memory expansion, we must first forbid loading in the high memory. We could bump up FSTHI, but that would loose the current value. It's therefore more clever to lower LSTHI:

    * This program forces the loader to load relocatable files in low memory
    AORG >2026
    DATA >A000 No more loading in high memory
    DATA >3000 Where to load in low memory (optional)
    * This program enables loading in high memory again.
    AORG >2026
    DATA >FFD7

    Preventing "undefined symbol" errors

    Before linking to a program, either from the RUN menu or from an auto-start file, the loader scans the symbol table for undefined labels, i.e. REFs that didn't get a matching DEF. In some cases, it could be an advantage to bypass this function.

    We could do this by just emptying the symbol table: it's a simple matter of reseting LSTLOW to its initial value. However, this will only work for auto-start files, as now any program name will cause a "program not found" error. But we could adjust LSTLOW so that it leaves the first label we loaded in the symbol table (or more than one if we wanted to, the important point is to cut off any REF).

    * This program empties the symbol table, but for 1 label
    * This prevents the loader from complaining about unresolved REFs
    AORG >202A This is LSTLOW (bottom of symbol table)
    DATA >3F30 Top is >3F38. Substract 8 bytes per label

    Enabling illegal tags

    The linking loader found in the cartridge only recognises a small subset of the possible tags generated by the TI assembler. All others result in an "illegal tag" error. We could write a set of loader improvements to deal with the missing tags. Illegal tags D, E, G, and H all branch at >25D8. So do tags P and above. Tags K to O have no fixed branch point since their vectors are overwritten by the first program loaded in the low memory expansion. We could cause them to branch anywhere in the loader between addressed >23F8 and >25F6, by just entering one byte per tag containing the offset in words from >23F8. To cause them all to branch at >25D8, we should use value >F0. Then of course, we should patch address >25D8 to process the tags we are interested in.

    Data segment

    For instance, the assembler allows for a data segment (a PC concept, it looks like this assembler was lifted from a PC assembler...). This segment does not have to contain only data, all it means is that it will be loaded at a different place than the rest of the program. It is often convenient to load data at a location and program at another, since data will generally be modified, whereas the program will only be read. For instance, you may want to "burn" a program into an EPROM at address >4000, but you must obviously maintain your data in RAM. To do this, enclose all your data between a DSEG and a DEND statement.

    We must now deal with the following new tags at loading time:
    Mxxxx$DATA 0000 At top of file: size of the data segment = xxxx.
    Sxxxx New loading address for data segment (xxxx=offset in data segment).
    Txxxx Reference to an address in the data segment from anywhere in the program (xxxx=offset in data segment).
    WxxxxAAAAAA0000 DEF of a label located in the data segment (name=AAAAAA, value=xxxx).
    XxxxxAAAAAA0001 Label REFerenced from inside the data segment (name=AAAAAA, ptr to first ref=xxxx).

    For the sake of simplicity, we're going to patch the tag checking routine so that any tag above F branches to our routine. We'll process the above tags or return to the loader for any other tag.

    * This program is a loader extension that deals with data segments
    * It processes the previously illegal tags M, S, T, W and X
    AORG >25D2 Patch the tag checking routine
    DATA >000F All tags above |F| will be illegal
    AORG >25D8
    B @NEWTAG Patch reaction to illegal tags

    AORG >2028
    DATA ENDPG Patch FSTLOW since our program will be here

    AORG >2676 Load this program just after the loader
    NEWTAG CI R3,>001C Tag value is in R3
    JEQ LDADR Tag |S| Loading address
    CI R3,>001D
    JEQ ADDR Tag |T| Address reference from CSEG
    CI R3,>0020
    JEQ DATDEF Tag |W| DEF in data segment
    CI R3,>0021
    JEQ DATREF Tag |X| REF in data segment
    CI R3,>0016
    JEQ DATSIZ Tag |M| Size of data segment
    CI R3,>0019 That was the old limit for legal tags
    B *R11 Let the loader deal with these

    ILLEG LI R0,>0A00 Error code 10 ("Illegal tag")
    B @>2432 That's what we overwrote with our patch

    DATSIZ MOV R8,@>202C |M| Save checksum
    BL @>2594 Read an integer from file
    INC R0 Size of data segment
    ANDI R0,>FFFE Make it even
    A @>2028,R0 Add current FSTLOW
    C R0,@>202A Compare with LSTLOW
    JHE TOOBIG Not enough room
    MOV R0,@TEMP Save for later
    LI R9,6 Name is always "$DATA "
    LP1 BL @>262E Skip these 6 chars
    DEC R9
    JNE LP1
    BL @>2594 Read an integer from file
    MOV 0,0 Should be 0 for data segment
    JNE ILLEG Could be non-0 if CSEG: illegal tag
    MOV @>2028,@DSEGPT Set data segment pointer
    MOV @TEMP,@>2028 New FSTLOW value
    B @>2400 Continue loading with next tag

    TOOBIG B @>2494 "Memory overflow" error

    LDADR MOV R8,@>202C |S| New loading address in DSEG
    BL @>2594 Read an integer from file
    A @DSEGPT,R0 Address in data segment
    B @>24B0 To address setting routine

    ADDR MOV R8,@>202C |T| Reference to a DSEG-relative address
    BL @>2594 Read an integer from file
    A @DSEGPT,R0 Address in data segment
    B @>24B6 To data loading

    DATDEF MOV R8,@>202C |W| DEF of a label located in DSEG
    BL @>2594 Read an integer from file
    A @DSEGPT,R0 Address of the label in data segment
    BL @>2566 Create new entry in symbol table
    MOV R0,@TEMP Save label value for later
    BL @>2594 Read integer
    MOV R0,R0 Should be 0 for DSEG
    JNE SK1
    MOV @TEMP,R0 Restore label value
    B @>2504 To DEF processing

    DATREF MOV R8,@>202C |X| REF to an external label from inside a DSEG
    BL @>2594 Read an integer from file
    A @DSEGPT,R0 Address of the first reference in data segment
    BL @>2566 Create new entry in symbol table
    MOV R0,@TEMP Save ptr for later
    BL @>2594 Read integer
    MOV R0,R0 Should be 0 for DSEG
    JNE SK1
    MOV @TEMP,R0 Restore ptr value
    B @>24C4 To REF processing

    SK1 B @>2400 Ignore other REFs/DEFs from other segments

    DSEGPT DATA 0 DSEG pointer
    TEMP DATA 0 Temporary buffer


    Loading that file enables the use of data segments: any file loaded after that one may contain DSEG sections that will be loaded in the low memory expansion.

    Loading multiple segments

    If you have a memory expansion device that performs bank switching, you may want to extend the above concept to common segments. All you have to do at programming time, is to split your program into (relatively) independent units that you declare as segments by enclosing them in CSEG segname .... instructions.

    A segment loader would check all the tag M at the top of the file and use them to arrange segments in the available banks. It should probably create a segment location table somewhere in memory, that will be used by your program to branch to a given segment.

    The loader will use tags N, P, W and X pretty much in the same way as described above for data segments. Except of course that is must read the segment number at the end of each tag to determine which segment must be accessed.

    The nice thing is, you don't need to re-write an assembler: just use the TI one and provide a special loader. Either by writing one from scratch, or by patching the existing loader as described above.

    Loading bias

    Sometimes you would like to load a program in the whole range of the low memory expansion. This is not possible, since it would cause the loader to overwrite itself. And if we load the program elsewhere, say at >A000, then save it into a memory -image file that loads at >2000, it won't work properly since all addresses will be wrong.

    Is there a solution (apart from writing a version of the loader that runs in the high memory)? Well, we could fool the loader into using a wrong offset value to adjust data when encountering a tag C. The problem is that this will also affect the setting of a new loading address by tag A, and the assembler issues a tag A at the beginning of each new record. We must therefore disable tag A first:

    * This program will be loaded at >A002, but is meant to run at >2000
    * REFs are not allowed yet
    AORG >266C
    DATA >045F Change the jump vector for tag |A| into tag |8|

    AORG >20E4
    DATA >2000 Change the content of loader's R5 (reloc offset)
    SLOAD EQU >2000 Where the program should run

    AORG >A000 Where we want to load it temporarily
    NOP AORG won't be issued unless followed by some code

    RORG Ignored upon loading, but needed to assemble
    SFIRST .... Put our program here
    SLAST  DATA 0                 This will be overwritten by the next file loaded 

    The AORG >A000 sets the loading pointer, that will remain unchanged throughout the RORG section since tag A is now disabled. Since the assembler disregards any AORG that is not followed by data, we need to load a dummy NOP at address >A000. Our program will therefore begin at >A002. Hence the final DATA 0, that will be overwritten by the next program being loaded (since the loader added the size of our program to FSTHI, which normally contains >A000, not >A002).

    A big problem remains: we cannot use REFs in our program as the reference solving routine uses R5 to find the next location to patch, based on the current one (each occurence of a REFerenced label points to the previous one). We could of course restore R5 at the end of our program, but then the DEFined labels would be all wrong. And we cannot place an AORG whithin the list of DEFs and REFs since the assembler groups them all at the end of the file.

    We must therefore use the REFerence solving routine to patch the loader. To do this, we'll use one of the pre-defined labels, say SPCHRD which is rarely used anyhow. We'll change its entry in the symbol table by negating the first word, so that it appears to be an unresolved REF. Then we'll change its value so that it points to R5 in the loader's workspace. Then all we have to do is to DEFine SPCHRD in our program: this value will be place in R5 by the REFerence solving routine. The solving routine will then proceed with the address found in R5, then with the address found at that address, until is finds a >0000 value. It is thus imperative that we stop the process by loading a >0000 value in the address pointed at by R5 (which is >2000 in our example).

    * This program is loaded at >A000, but is meant to run at >2000
    * The SAVE utility will handle it accordingly

    AORG >266C
    DATA >045F Change the jump vector for tag "A" into tag "8"

    AORG >20E4
    DATA >2000 Change the content of loader's R5 (rel offset)

    AORG >A000 Where we want to load it temporarily
    NOP AORG won't be issued unless followed by code

    DEF SLOAD This DEF will be biased (i.e. >2000)
    DEF SPCHRD Cancel bias now
    DEF SFIRST,SLAST These will have the real address (>A002, etc)
    REF SPCHWT For test purposes: this REF will work normally
    ABS @SLOAD Silly test program: ABS @>2000
    NEG @SFIRST NEG @>2000
    CLR @SPCHWT CLR @>9400
    B *R11
    DATA 0 This will be overwritten by the next program loaded
    * This causes the DEF SPCHRD to cancel the load bias
    AORG >3F78 Point at entry for label SPCHRD
    DATA >ACB0 That's "SP" negated: this label is now an unresolved REF
    AORG >3F7E Point at value of SPCHRD
    DATA >20E4 Link to the next occurence: this will be the loader's R5

    AORG >2000
    DATA >0000 Stop the reference solving (since R5 now contains >2000)
    SPCHRD EQU >A002 Value that will be placed in R5 (>A000 +2 for the NOP)

    * The liker will complain since we changed the value in >2000 ("program not found")
    * Therefore load this program just after the above one to restore the flag value in >2000
    AORG >2000
    DATA >A55A

    Load these two programs, then load the SAVE utility. It will save the first program from the high memory expansion, into an EA5 file that will load and run in the low memory expansion.

    Extra assembler opcodes

    By editing the ASSM1 file, I found out that the assembler can recognize (and issue data for) a number of opcodes corresponding to machine language instructions that are supposedly illegal with the TMS9900. This is probably due to the fact that this assembler is able to produce programs meant to run on other systems, such as the 990 minicomputer, the TMS9940-based systems, TMS99000 or 9989 systems.

    The opcodes in the first group are in format VII, which means they do not take any operand.
    laeco represent the status bits affected: logically higher, arithmetically greater, equal, carry and overflow

    Value Opcode Status Meaning
    >0C00 CRI laeco Convert Real to Integer
    >0C01 CDI laeco Convert Decimal to Integer
    >0C02 NEGR lae Negate Real
    >0C03 - - (exists, but not encoded by the assembler)
    >0C04 CRE laeco Convert Real to Extended integer
    >0C05 CDE laeco Convert Decimal to Extended integer
    >0C06 CER laeco Convert Extended integer to Real
    >0C07 CED laeco Convert Extended integer to Decimal
    >0C08-0C0D - (exist, but not encoded by the assembler)
    >0C0E XIT eXIT the floating point interpreter

    The opcodes in the second group are in format VI, i.e they take one operand in any of the general addressing modes.
    Value Opcode Status Meaning
    >0780 LDS Long Distance Source
    >07C0 LDD Long Distance Destination
    >0C40 AR     laeco  Add Real
    >0C80 CIR laeco Convert Integer to Real
    >0CC0 SR laeco Substract Real
    >0D00 MR laeco Multiply Real
    >0D40 DR laeco Divide Real
    >0D80 LR lae Load Real
    >0DC0 STR lae Store Real
    >0E00 - (not encoded by the assembler assembler, but some exist)
    >0E40 AD laeco Add Decimal
    >0E80 CID laeco Convert Integer to Decimal
    >0EC0 SD laeco Substract Decimal
    >0F00 MD laeco Multiply Decimal
    >0F40 DD laeco Divide Decimal
    >0F80 LD lae Load Decimal
    >0FC0 STD lae Store Decimal

    All opcodes dealing with Reals are meant for TMS99000-based systems that use a 99110A CPU and for the 9989. They are designed to provide a floating point package.

    The Decimal and Extended integer opcodes are found on the 9989. They provide an easy-to-use BCD interface.

    LDS and LDD are meant for 990/10 mainframe systems, for 99000-based systems and for the 9989. They are designed to support the TMS99610 memory mapper, to allow easy access from one page to another without the need for the user to switch pages.

    Finally, there are a few more:

    Value Opcode Format Meaning
    >2C00 DCA IX Decimal Correct for Addition (= XOP 0)
    >2C40 DCS IX Decimal Correct for Substraction (=XOP 1)
    >2C80 LIIM IX Load Immediate Interrupt Mask (= XOP 2)
    >0320 LMF X Load Memory-map File

    The first three are aliases for XOP instructions. They are meant for use with a 9940 CPU. This CPU only allows 4 levels of interrupts and therefore cannot use LIMI (which allows 16 levels). Hence the special LIIM instructions that takes a number from 0 to 3 as an argument. DCA and DCS take one argument, in any of the general addressing mode. You can use them as shortcuts for XOP 0 and XOP 1 on the TI-99/4A, if you feel like it.

    LMF takes two operands: a register and a number that can be 0 or 1. It is used by the TMS99000, but I don't know what for.

    Not assembled opcodes

    The assembler will not produce the following opcodes, although they can be used on the 9989 and often also on the 99000. Formats I-IX are the standard formats we know, formats X-XXI are unique to these special opcodes and are only used by the TI990/40 minicomputer.
    laeco represent the status bits affected: logically higher, arithmetically greater, equal, carry and overflow

    Value Opcode Format Status Meaning
    >0000-001B - (no opcodes)
    >001C SRAM XIII laec Shift Right Arithmetic Multiple
    >001D SLAM XIII laeco Shift Left Arithmetic Multiple
    >001E RTO XI e Right Test for One
    >001F LTO XI e Left Test for One
    >0020 CNTO XI e Count Ones
    >0021 SLSL XX e Search LiSt Logical address
    >0022 SLSP XX e Search LiSt Physical address
    >0023 BDC XI lae o Binary to Decimal ascii Conversion
    >0024 DBC XI lae o Decimal ascii to Binary Conversion
    >0025 SWPM XI lae SWaP Multiple precision
    >0026 XORM XI lae eXclusive OR Multiple precision
    >0027 ORM XI lae OR Multiple precision
    >0028 ANDM XI lae AND Multiple precision
    >0029 AM XI lae Add Multiple
    >002A SM XI lae Substract Multiple
    >002B MOVA XIX lae MOVe Address
    >002C - no opcode
    >002D EMD VII (all) Execute Micro Diagnostic
    >002E EINT VII Enable INTerrupts
    >002F DINT VII Disable INTerrupts
    >0030 STPC VIII Store Program Counter
    >0040 CS XII lae Compare String
    >0050 SEQB XII lae Search string for EQual Byte
    >0060 MOVS XII lae MOVe String
    >0070 LIM VIII (mask) Load Interrupt Mask from register
    >0080 LST VIII (all) Load Status from register
    >0090 LWP VIII Load Workspace Pointer from register
    >00A0 LCS VIII Load writable Control Store
    >00B0 BLSK VIII Branch immediate and push Link to StacK
    >00C0 MVSR XII lae MOVe String Reverse
    >00D0 MVSK XII lae MOVe String from StacK
    >00E0 POPS XII lae POP String from stack
    >00F0 PSHS XII lae PuSH String to stack
    >0100 EVAD VI EValuate ADdress instruction
    >0140 BIND VI Branch INDirect
    >0180 DIVS VI lea o Divide-Signed
    >01C0 MPYS VI lae Multiply-Signed
    >0301 CR ?? ????? Compare Reals
    >0302 MM ?? ????? Multiply Multiple
    >0303-031F - (no opcodes)
    >03F0 EP     XXI          Extended Precision
    >0C03 NEGD   VII   lae    Negate Decimal
    >0C08 NRM XI lae Normalize
    >0C09 TMB XIV e Test Memory Bit
    >0C0A TCMB XIV e Test and Clear Memory Bit
    >0C0B TSMB XIV e Test and Set Memory Bit
    >0C0C SRJ XVII Substract from Register and Jump
    >0C0D ARJ XVII Add to register and Jump
    >0C0F - no opcode
    >0C10 INSF XVI lae Insert Field
    >0C20 XV XVI lae eXtract Value
    >0C30 XF XVI lae eXtract Field
    >0E00 IOF    XV           Invert Order of Field
    >0E01 SNEB XII lae Search string for Not Equal Byte
    >0E02 CRC XII e Cyclic Redundancy Code calculation
    >0E03 TS XII lae Translate String
    >0E04-0E3F - (no opcodes)

    If you have any insight on what these opcodes are good at, please let me know.

    File formats

    Memory-image EA5 files

    These "program" files contain a mere dump of the memory content. There is only a 3-word header that contains instructions for the loader. Normally, this will be option 5 of the Editor/Assembler cartridge, hence the name EA5. But there are other loaders around: you can even download one from this website (MILD).

    The header structure is the following:

    Address Content
    >0000 Flag. >0000 = last file. >FFFF = load one more file
    >0002 Address where to load the program.
    >0004 Number of bytes to load (not counting these 6).

    The loader loads the specified number of bytes, taken directly after to the header, to the specified address in memory. If the flag word in >FFFF, the loader then loads another file whose name is coined by incrementing by 1 the last character of the current file name. This process goes on until a file with a >0000 flag is loaded. At this point, the loader executes the program by performing a BL to the address where the first program was loaded.

    The workspace upon entry will be >20BA with the Editor/Assembler cartridge, but the program should not take this for granted since other loaders may use a different workspace. Similarly, it may be wise for a program to properly setup the VDP memory, rather than to assume that the Editor/Assembler cartridge has already done it.

    A program can return to the caller with B *R11, or reset the TI-99/4A with BLWP @>0000.

    Tagged-object code files

    These Div/Fix 80 files are produced by the assembler and used by the linking loader to place a program in memory. They are more bulky and slow to load than EA5 files, but have two main advantages:

    All this is achieved by interlacing the data words with special characters called "tags". A tag is nothing else than an instruction for the loader. Almost all tags are followed with a word of data, sometimes by a string or an additional word. There are two file formats, compressed and uncompressed, determined by the C option of the assembler. In compressed files, data words are passed as integers, and no checksum nor record number is issued. In uncompressed mode, the numbered are "spelled out" as 4-character hexadecimal strings. This has the advantage that the file can be edited with the Editor without having to re-assemble the source file.

    Below are all the tags I'm aware of. Not all of them can be issued by the assembler provided with the Editor/Assembler cartridge.

    Tag Data Segment Meaning
    0 ####$$$$$$$$ PSEG At top of file. ####: size of the program segment.
    $$$$$$$$: its name (empty unless renamed with the IDT instruction).
    1 #### AORG Auto-start file at absolute address ####
    2 #### PSEG Auto-start file at offset #### in the program segment.
    3 ####$$$$$$ PSEG Reference to a REF label from a program segment. $$$$$$: label name
    #### offset of the last address referencing this label. At end of file.
    4 ####$$$$$$ AORG Reference to a REF label inside an absolute section. $$$$$$: label name
    #### last address referencing this label. At end of file.
    5 ####$$$$$$ PSEG DEFinition of a label located in a program segment. $$$$$$: label name
    #### offset of the label in the segment. At end of file.
    6 ####$$$$$$ AORG DEFinition of a label located in an absolute section, or an EQUated label.
    $$$$$$: label name, #### label value (e.g. absolute address). At end of file.
    7 #### all Checksum. ####: negated sum of all bytes in the record upto tag 7.
    8 ! #### all Ignore the number ####. Used to "comment out" a checksum.
    9 #### AORG ####: new address where to load data.
    A #### PSEG ####: new offset in the program segment where to load data.
    B #### all Load data word #### at the current address (then increment the pointer)
    C #### all Add PSEG offset to word #### and load it in memory.
    D *! #### all but AORG Replaces the relocatable offset with #### .
    E *! nnnn#### all Adds #### to a REF when resolving it. nnnn is the number of the REF.
    F . all End of record. Optionally followed by a right-justified record number.
    G *! ####$$$$$$ PSEG Symbol table dump. $$$$$$: label name ###: value
    H *! ####$$$$$$ AORG Symbol table dump. $$$$$$: label name ###: value
    I ! $$$$$$$$ all Program ID (used with symbol table dump).
    J ! ####$$$$$$0xxx
    or 000t
    DSEG, CSEG Normally, symbol table dump. $$$$$$: label name ###: value. xxx: segment.
    But the TI loader uses tt as the next tag (t in uncompressed mode)
    K *! ####$$$$$$ ? External macro reference.
    M * ####$DATA 0000
    At top of file. ####: size of the data segment,
    of the blank common segment (CSEG with no name),
    or of the common segment named $$$$$$, number xxx assigned by assembler.
    N * ####0xxx all Add the address of common segment xxx to word #### and load it in memory.
    P * ####0xxx CSEG ####: new offset in common segment xxx where to load data.
    Q *! ####nnnn ? COBOL segment reference. ####: record offset. nnnn:CBSEG #.
    R *! ####nnnn ? Repeat count. ####: value. nnnn: count.
    S * #### DSEG ####: new offset in the data segment where to load data.
    T * #### DSEG Add DSEG offset to word #### and load it in memory.
    U * 0000$$$$$$ all Issued by the LOAD instruction. $$$$$$: label name.
    V * ####$$$$$$ PSEG SREF to a label, matching DEF is not required. $$$$$$: label name
    W * ####$$$$$$0000
    DEFinition of a label located in the data/common segment. $$$$$$: label name
    #### offset of the label in segment xxx. At end of file.
    X * ####$$$$$$0000
    Reference to a REF label from a data/common segment. $$$$$$: label name
    #### offset of the last address referencing this label. At end of file.
    Y * #### AORG SREF to a label, matching DEF is not required. $$$$$$: label name
    Z * ####0000
    SREF to a label, matching DEF is not required. $$$$$$: label name
    xxx: segment number.
    : copyrights string . End of file. Ignore copyright string and following records, if any.

    * These tags are not accepted by the standard loader provided in the Editor/Assembler cartridge.
    ! These tags are not issued by the standard assembler, as far as I know.
    #### In compressed mode: 2-byte integer. In uncompressed mode: string of 4 hex digits 0-9, A-F. Ditto for nnnn.
    0xxx Segment number, from 0 (DSEG) to 127. Compressed: 2 bytes, uncompressed: 4 hex digits.
    $ Any ascii character. Not affected by compression mode.


    Tags 0 and M are used by the loader to find a free slot in memory where to load a given segment. The total size of the segments is passed as an argument together with the segment name. Note that the names of the data and the "blank-common" segments are predefined ($DATA and $BLANK), whereas the name of the program segment can be defined with the IDT assembly instruction (by default, it's a string of 8 spaces). Other common segments can be specified by placing their name after the CSEG instruction in the assembly program. Tag M is followed by the number of the segment: >0000 for the data segment, >0001 for the blank common segment (i.e. when no name is specified after CSEG), and higher numbers for all other common segments.

    There can thus be at least three type of relocatable segments: program, data and common segments that can be loaded at different memory locations. All the PSEG sections in a file will be grouped together inside the program segment, all DSEG inside the data segment and all CSEG inside the corresponding common segments. AORG sections are always loaded at the specified address and the loader therefore has no need to know their size.

    Note that the loader in the Editor/Assembler cartridge cannot handle the data nor the common segments.

    Loading data

    Tags 9, A, S and P are used to specify a loading address. Tag 9 passes the address as such. The others pass an offset within the program, data or common segment respectively. The loader must add the address of the beginning of that segment to the offset to obtain the actual address. Note that tag P comprises an additional number that specifies the number of the common segment to be used.

    The loader in the cartridge only recognises tag 9 and A. It loads relocatable segments in the high memory expansion first, then in the low memory expansion and maintains a pointer to the next available space, that will be used as a load offset for the next file. Tag D can be used to override this offset by a user-specified value. This tag isn't produced by the assembler, but is meant for use when editing the code file.

    Tag B copies data as such into memory. Most of a program will consists of data that can be passed by tag B. The only exceptions are instruction whose operand is a label located in a relocatable segment, whether program, data or common. E.g. CLR @COUNT or BL @SUB1, assuming COUNT is in the data segment and SUB1 in the program segment. The assembler does not know where these segments will be located, but it knows the offset of a label with respect to the beginning of the segment. Therefore, it issues a tag C, T or N which tells the loader to add the address of the program, data or common segment respectively to the data word before to load it into memory. Here also, tag N specifies the number of the common segment to use.


    Tag 6 is used to define a label. The value of the label and its name are passed together with the tag. Such labels could be addresses in an absolute section, or values defined with an EQU statement. By contrast, tag 5 and W are used to specify labels corresponding to an offset in the program, data or common segment (W is shared by data and common segment: an extra word is passed to determine which segment must be used). Here again, the loader adds the base address of the adequate segment to specified offset and places the label in the symbol table, thereby possibly solving any pre-existing REFs.

    Tag 4, 3 and X are used to REFerence external labels (i.e. labels DEFined in another file) from inside an absolute section, a program, a data or a common segment (X is shared by data and common: an extra word containing the segment number determines which is which). The accompanying data corresponds to the offset (or the absolute address with tag 4) of the last place in the segment where this label is used. If the loader knows the value of this label, it places it at the pointed location. Otherwise it places the label in the symbol table (and negates the first 2 chars) and waits for a DEF to the same label to arrive, by which time it will solve the REF.

    Since it would use up a lot of memory to have a tag for each memory word that uses an external label, the assembler uses a special trick. There is only one REF per label (per file), and it points to the last address where the label is used. The content of this address, that will be replaced with the label value, contains a pointer to the previous address where the label was used. This pointer is an absolute address with tag 4, an offset with tag 3 and X. That address in turn contains a pointer to the previous one, etc. The last address contains a >0000 word with a tag B to mark the end of the chain. All the loader has to do is to walk the chain, replacing each pointer with the value of the label.

    Offset      Program          Object code (uncompressed, tag in bold)
    IDT 'PLAYBOYS' 0000CPLAYBOYS (size and name of PSEG)
    >0000 CLR @TEST B04E0B0000<---+ (end of REF chain)
    >0004 SETO @TEST B0720C0002----+
    >0008 DATA TEST C0006--^ <---+
    >000A ABS @TEST B0760C0008-----+ <--+
    END 3000CTEST F---------+ points to last use of TEST

    Tag V is issued by the SREF instruction and is equivalent to tag 3. The only difference is that it will not generate an "undefined symbol" error number >0D if no matching DEF was provided by the time the program is launched. This can be useful if your program comprises optional modules. All you must do is to check the first occurence of this label in your program to see if a value was provided by the loader: if it contains >0000 the optional module was not loaded. Note that this tag is not supported by the standard loader.

    Tag Y does the same for SREFs included in an absolute section, tag Z for SREF in a DSEG or CSEG segment.

    * This demonstrate the use of SREF  
    * PRINT is a procedure in a optional extra file
    SREF PRINT Reference it, but don't check for a DEF
           MOV  @HERE+2,R0
    JEQ NOPE The extra file was not loaded
    HERE BL @PRINT The second word is >0000 before linking
    NOPE ...

    MOV @HERE+2,R0
    JEQ $+4 Skip if not loaded
    BL @PRINT The 2nd word is not >0000: it points at HERE+2

    Tag U is an oddball. It is issued by the assembly instruction LOAD, whose operand is a label. Contrarily to the other tags dealing with labels, that are grouped at the end of the file, tag U appears in the program at the position it was inserted in the source file. The value of the LOADed label is always >0000. Appearantly this is meant as a dummy DEF, used to force loading of a label in the symbol table (possibly to implement #ifdef and #ifnotdef statements?). It is not supported by the standard loader anyway (but it could be useful to implement a fancy loader and pass loading commands without having to re-write the assembler...).

    Tag E is another weird one. As far as I know, it is not issued by the assembler and is not recognized by the loader. It serves to add an absolute value to a REF symbol. It is followed by two words of data: the second is to value to be added, the first one is the number of the REF symbol to be modified. REF symbols are counted from 0, in the order they appear in the code file, whether the are preceded by a tag 3, 4, V, X, or Y. When resolving the REF chain, the specifed value should be added to the DEFined one.

    Tag K is an external macro REF (whatever this means). It has the same syntax as tag 3 but is not issued by the assembler, not recognized by the standard loader.


    Tag 1 and 2 are used by auto-start files. The loader saves the address they provide in word >2022 (with tag 2, it adds the address of the program segment to the specified offset). Once loading is completed, i.e. a tag : is encountered, the loader begins execution at this address. That is, provided there are no REF labels that were not solved by a matching DEF.

    To generate a tag 1 or 2, you place a label in the operand field after the END instruction: END START

    Record info

    Tag F marks the end of each record, any following byte in this record is ignored. With uncompressed files the last 4 bytes in the record contain a decimal record number.

    Tag : signals the end of the file. Any extra byte on this record are ignored, so is any additional record.

    Tag 7 is used to verify the integrity of a record. Both the assembler and the loader perform the same calculation on each record: they add up all bytes in the record, upto and including the tag 7 itself. Then the assembler negates the resulting word and passes it with a tag 7 in uncompressed files. The loader just adds this value to the checksum it has calculated: if the result is not zero the record has been tempered with and a loading error occurs.

    Tag 8 is not issued by the assembler. It is useful for us as it allows to comment out any tagged word. Most often this will be to replace tag 7 and prevent verification of the checksum.

    Tag I is issued by the SYMT directive, which does not work with the TI assembler: it includes the program ID in the output file. The loader recognises it, and just skips the next 8 characters.


    The following tags are not issued by the assembler, as far as I know. They were meant for other assembler, such as the model 990 computer assembler.

    Tag GH and J are used to include a copy of the whole symbol table within the output file. This is triggered by the SYMT directive, which is not supported by the assembler included in the Editor/Assembler module. Tag G would be used to list relocatable symbols, tag H for absolute symbols and tag J for data or common segment symbols.

    The loader does recognise tag J, but in a very stange way: it uses the second byte of data as a tag (or the last hex digit with uncompressed files). I have no idea whether this is of any use or if it's just a bug, since it does not match the expected syntax for tag J.

    Tag Q references a Cobol segment. It is followed by the record offset and the Cobol segment number.

    Tag R specifies a repeat count. It is followed by a value and the number of repeats.

    I do not know the meanings of the remaining tags: L, O, nor of any tag beyond Z, if any.

    If you can provide any information on these, by all means let me know.

    Revision 1. 6/22/99 Ok to release
    Revision II. 9/5/99 Added non-TI99 opcodes. Added DF80 tag D + K. CSEG discussed.
    Revision III. 1/7/01 Added tags E,G,H,K,Q,R,Y,Z.

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