Summary

Adapter board to use a flash chip for the system rom in a NEC PC-8300, PC-8401, PC-8500, or anything else that has a 23C1000 mask rom.

PCB: OSHPark or PCBWAY

BOM: https://www.digikey.com/short/z8293n

Source: https://github.com/bkw777/aDIPters

References

File:UPD23C1000A.pdf

File:MX23C1000.pdf

Pinout comparison:

  +-----------------------------------------+------ MX27C1000 / 27C010 / 28F010 / *(29F010)
  |    +------------------------------+---- | ----- NEC 27C1000 / Hitachi HN27C301
  |    |        +------------+------- | --- | ----- 23C1000 (NEC uPD23C1000, NEC D23C1000C, Macronix MX23C1000)
  |    |        |            |        |     |
  |    |        |            |        |     |
                |            |   
*(NC) VPP  1    |            |   32  VCC
 A16  OE/  2                     31  PGM/
           3   A15  1   28  VCC  30        NC
           4   A12  2   27  A14  29
           5   A7   3   26  A13  28
           6   A6   4   25  A8   27
           7   A5   5   24  A9   26
           8   A4   6   23  A11  25
           9   A3   7   22  A16  24        OE/
           10  A2   8   21  A10  23
           11  A1   9   20  CE/  22
           12  A0  10   19  D7   21
           13  D0  11   18  D6   20
           14  D1  12   17  D5   19
           15  D2  13   16  D4   18
           16  GND 14   15  D3   17

Compatible flash/eeprom/eprom chips that can be used on this board (LCC or TSOP)

Without R3 installed:

39SF010 https://www.digikey.com/short/z88hb8

29SF010

29EE010 https://mou.sr/39tR5zu

29F010

28C010

With R3 installed (10k-47K):

28F010

27SF010

27C010

Any speed and any temperature range is ok.

Any TSOP32 or LCC32(7x9) package is ok.

ROM images

NEC PC-8300 system rom: File:831000-438.bin

NEC PC-8300 system rom, Y2K patched: File:831000-438-y2k.bin

Directions

Building

See FlexROM_100 to see how to do the dip legs.
Search youtube for "drag solder" to see how to solder the TSOP legs with an ordinary soldering iron.

Suggest installing parts in this order:

Legs - The holes for the the legs are intentionally small and a fairly close fit on the legs. The legs should be installed first to avoid the problem where if you accidentally get solder in some of the holes while soldering the other parts near by, it can be difficult to wick the holes clean enough to insert the legs after that without vacuum.
R1, R2
TSOP or PLCC chip
Jumper pins - Flush-cut the posts on the bottom of the board after soldering.

You don't install R3 usually. It is for VPP on pin 1, to support EEPROM/EPROM devices that have a VPP pin. These are all old devices that aren't made any more, but you can still buy used and new-old-stock. Don't install R3 if you're using the SST39SF010A part in the BOM linked above, or any 29 or 39 series flash chip. But if you happen to already have a 28F010, 28SF010, 27SF010, 27C010 etc, you can use it instead of the 39SF010, and if so, you need to install R3. 47K the same as the others.

Programming

Requirements:

eprom programmer, such as TL-866

To program the chip,

Move the jumper to PRG
Put the board into a programmers' ZIF socket as if the whole board were a DIP chip
Tell the programmer software that it is the PLCC version of whatever chip is soldered on the board

 minipro -p "SST39SF010A" -w 831000-438-y2k.bin

Install

Move the jumper to RUN

Put the board in the ROM0 socket in the PC-8300, or IC24 in PC-8401, or IC9 in PC-8500.

leave pins 1, 2, 31, 32 outside the socket, pretend the white silskreen line is the pin-1 / pin-28 end of a dip-28 chip.

for PC-8401, cut pin 1 a little short so that it doesn't touch R65, or use the DIP-28 version of the board (see FLASH_23C1000_DIP28 from github.com/bkw777/aDIPters)

Press Shift-CTRL-Reset to hard-reset the PC-8300 to force it to load the new rom, including re-reading the one-time power-on defaults. If the date says 2000, then you got it. If the date says 1983 or 2083, then you didn't do a full reset.

FLASH 23C1000

Contents