IDE interface card prototype


A fine mess o' wires, isn't it? And yet it works!

Blow-up of IDE prototype board

PE-box connector

  • Connections #2 to 60 on this side, connections #1 to 59 on back side (small PCB glued to the prototyping board).
  • 244: three 8-bit buffers, 74LS244 for the address bus and control lines (74LS245 would also do).
  • 245: A 8-bit transceiver, 74LS245 for the data bus.
  • 125: A quad 74LS125 buffers, for 3-state output signals (RDBENA* and EXTINT*).
  • 7805: A voltage regulator, 7805CT, +5 volts, 1 Amp. A 22 uF cap is located under then lower part of the heat sink.

    • CRU logic

  • 85: A 4-bit comparator, 74LS85 to compare the CRU address to that set on the DIP-switch.
  • DIP: Dual-in-line 7-switch package (only 5 are used). Note the blue 4.7K pull-up resistor network.
  • 259: An 8-bit addressable latch, 74LS259 for CRU output operations
  • 251: An 8-to-1 multiplexer, 74LS251 for CRU input operations (unbuffered CRUIN line to the PE-box).
  • LEDs: A yellow light-emitting diode reacts to CRU bit 0, a red one to IDE access. A 270 ohm resistor for each.

    • Address selection logic

  • 138: A 3-to-8 decoder, 74LS138 does most of the work.
  • 688: An 8-bit comparator, 74LS688 to detect the register mapping area (>4000-40FF).
  • 139: Half a dual 2-to-4 decoder, to select among the devices: clock / SRAM / IDE port1 / port3
  • Sw: Main switch. Prevents the card to answer to CRU commands, hence to memory operations (which need bit 0).

    • Static RAM

  • 628512: A 512 kbytes SRAM, HM628512ALP-5 to store the DSRs and the file buffers (upside-down).
  • 373: An 8-bit latch, 74LS373, to store a page number for the SRAM.
  • Eight 4.7K pull-down resistors, to select page 0 when the '373 is in high impedance state.

    • Clock

  • A RTC65271 real-time clock, with 4 Kbytes of SRAM and an on-chip crystal (upside-down).
  • Two +3 volts, BR1225 batteries in an on-chip battery holder.

    • Bus demultiplexer (8 <=>16 bits)

  • 139: Half a dual 2-to-4 decoder to decode read/write on odd/even bytes operations.
  • 244: An 8-bit buffer, to read odd bytes from the IDE ports.
  • 373: Two 8-bit latch, 74LS373, to latch odd bytes upon writing and even bytes upon reading.
  • 245: An 8-bit transceiver, to write the even byte to IDE ports (historical reasons: should be a 74LS244).
  • IDE connector: pins # 1 and 40 indicated. Pin #20 (key) removed to prevent wrong connections.
  • Insert: IDE cable, to connect two drives. Hole #20 plugged to prevent upside-down connections.

    • Pulse generator

    165: A 74LS165 shift registers produces WR* and RD* pulses for the IDE controller.

    Logic gates (used in parts by the above sections)

  • 32: Two quad OR gates, 74LS32.
  • 02: A quad NOR gates, 74LS02.
  • 08: A quad AND gates, 74LS08.
  • 04: Two hex inverters, 74LS04.

    • Note the tiny yellow bypass cap (100 nF) above each chip

    Color code

  • Red: unbuffered signals
  • Orange: address bus. Orange/white: signals derived from address lines.
  • Green: 8-bit data bus. Green/white: least significant byte in 16-bit bus.
  • Blue: CRU bit lines. Blue/white: signals derived from CRU bits.
  • Brown: Control lines (RDBIN, MEMEN*, etc). Brown/white: signals derived from control lines.
  • Black: power lines

    • Revision 1. 5/24/00. Preliminary, not for release.
    Revision 2. 8/26/01. New dempx, pulse generator. OK to release.


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