Bill of Materials

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Tested configurations and suggested replacements:

• • Logic:

    • Tested configurations:

      • All logic ICs, with exception of 74LS06, 74LS92, and 74LS670 are 74ALS family.

      • All logic ICs, with exception of U30 are 74LS family. U30 is 74S74.

      • Most logic ICs are 74AHCT or 74HCT. Using 74ACT for buffers and transceivers, and following TTL parts: 74LS06, 74LS92, 74LS670.

    • Suggested replacements:

      • TTL: 74ALS, 74LS, 74F families. 74F is recommended for buffers and transceivers - '573, '245 and '244 parts

      • CMOS with TTL compatible inputs: 74AHCT, 74HCT, 74ACT families 74ACT is recommended for buffers and transceivers - '573, '245 and '244 parts.

      • It is not recommended to use non-TTL compatible CMOS logic families like 74HC, 74AHC or 74AC.

      • For reliable operation on higher frequencies (more than 4.77MHz) U30 ('74 D flip-flop) must use a high speed logic, for example 74ALS74, 74F74, 74S74 or 74AHCT74.

  • CPU:

    • Tested configurations:

      • 12 MHz: NEC uPD70108HCZ-16 (NEC V20HL)

      • 10 MHz: NEC uPD70108HCZ-10 (NEC V20HL), NEC uPD70108C-10 (NEC V20), 8088-1 (AMD and Siemens)

      • 8 MHz: NEC uPD70108C-8 (NEC V20), 80C88-2 (Intel and Harris), 8088-2 (Intel, Fujitsu, Siemens)

      • 4.77 MHz: 80C88 (Harris), 8088 (Intel, NEC, Soviet clones).

      • Note: I observed some stability issue with Intel 8088 parts. This is apparently due to noise on power rails. Possible mitigation: Replacing logic with 74AHCT/74HCT series, soldering axial decoupling capacitors directly to ICs' power pins on the solder side of the PCB, using a different power supply. I did not have this issue when using Intel 8088-2 or 8088 of other manufacturers.

    • Suggested replacements:

      • Any 8088-compatible CPU in DIP40 package.

      • NEC V20HL is recommended for high performance, low power consumption, and supporting 80186+ instructions.

  • Intel 82xx series ICs  (except of U9)

    • Tested configurations:

      • Intersil 82Cxx CMOS parts. Work very stable up to 13.3 MHz, with exception of DMAC. Intersil C82C37-5 DMA has stability issues when used together with TTL logic. It works fine with 74AHCT/74HCT logic.

      • Intel, OKI and NEC 82Cxx CMOS parts. Work very stable up to 8 MHz.

      • Intel, AMD and NEC 82xx nMOS/bipolar parts. Work stable up to 8 MHz, except of AMD 8288 bus controller.

    • Suggested replacements:

      • CMOS (82Cxx) parts are recommended.

      • TTL/NMOS parts work too, but they consume much more power and get much hotter.

      • Note: AMD 8288 bus controller is not recommended (it has different timing specifications than 8288 chips of other manufacturers).

      • Note: NEC uPD8237AC-5 DMAC and NEC uPB8288D bus controller seem to be most stable at higher frequencies.

  • Keyboard controller (U9)

    • Tested components:

      • VIA VT82C42N

      • Holtek HT6542B

      • Intel P8042AHP with AMI KB-BIOS-VER-F firmware

  • RTC (U10):

    • DS12885 is the recommended part.

    • DS12C887A or DS12887A RTCs. In this case X2 crystal and BT1 battery holder are not required. The downside of it - when the battery inside the RTC module dies, the entire RTC module must be replaced.

    • DS12C887 and DS12887 are not recommended, since they don't support RAM clear function.

  • Flash memory:

    • 29F010/29C010 ICs should be used.

    • The board provides 17-bit address to the flash memory, so it can address 128 KiB. It is possible to use larger flash memory chips, like 256 KiB (29F020) or 512 KiB (29F040) chips, in this case higher address pins (A17 - pin 30, and A18 - pin 1) should be connected to the ground.

  • Minimal system configuration (might require BIOS tweaks):

    • Only one SRAM chip (U11). This limits system memory to 512 KiB. U27 and U35 are not required in this case, and two positions DIP switch could be used (connected to pins 7-10).

    • Only one PIC (U5). In this case IR2 (pin 20) of U5 should be connected to IRQ9 input on ISA bus (or pin 19 of U6). This limits number of system interrupts to 8, and it won't be possible to use PS/2 mouse, RTC wake-up interrupt and NPU error reporting using interrupt 13h.

    • No RTC (U10). This will definitely require BIOS modifications.

    • No PS/2 mouse support. P2, C49 and C50 are not required in this case. J3-J5

    • 8087 math coprocessor is completely optional. In fact very few IBM PC or IBM PC/XT machines had a coprocessor, so not many programs rely on it.

    • On-board LEDs (D1, D2) and reset switch (SW1) are optional.

  • Remarks for the Bill of Materials list

    • Suppliers and part numbers recommendations are based on my own findings, and they are certainly not complete, and even may contain some errors. There are many more electronic components suppliers, and it is possible that you'll find better deals elsewhere.

    • Question mark (?) after part number means that component should be compatible according to its description, but I never ordered one, and so I was not able to confirm its compatibility. Please double check before ordering.

    • Asterisk (*) after quantity means that component is optional in certain conditions. Please read notes for more information.