Improved 512K RAM and 512K ROM module


Original discussion here:!topic/retro-comp/l4A5oCAnMMQ

Rev1 is a “hobbyist-friendly” design with all through-hole components.


  • ROM emulation, with few jumper configurations, the ROM socket can be populated with RAM and data uploaded into the RAM via serial port at 115200 baud,
  • EPROM programmer, programming software can be loaded in RAM to program the EPROM,
  • A serial port, the same serial port used to load ROM image can be reuse as a regular serial port.
  • A real-time clock like PCF8563 that can generate 32Hz output driving the interrupt,
  • Battery backup for RAM & RTC,
  • SPI port,
  • Faster, should be able to run 20MHz
  • Cheaper, the board should be around $50.


Design Information


Gerber photoplot

CPLD equations

Bill of Materials


EPROM Programmer


By enable the serial bootstrap ROM on CPLD, the 512K RAM/ROM, in conjunction with a Z80 CPU board, can serve as a EPROM programmer. The following instruction is for programming SST39SF040 EPROM.

The jumper configuration of RR512K is

  • T24 jumper to ground
  • T22 jumper to ground
  • T25 jumper to T27
  • T26 jumper to T28

Insert a SST39SF040 in the FLASH socket (U2),

Connect a serial port to connector P2 and set baud rate to 115200 N-8-1,

Power up the board and send the serial loader, serload.bin to the serial port. serload.bin is a binary file so be sure to check the 'Binary' box,

The EPROM programmer will respond with:

RR512K Loader v0.1 4/21/20
Auto start at 0xB400

Next send the EPROM programmer, progSST39F040.hex. The console will respond with:

Programmer for SST39SF040 ver 0.2 4/23/20
SST39SF040 will now be erased
Enter Y to proceed, all other keys to abort

Enter 'Y' (upper case Y) to chip erase SST39SF040 EPROM or any other character to cancel the operation. Once chip is erased, the program will prompt user to send the image file in Intel Hex format:

SST39SF040 erased, ready to upload the image file
(truncated) ………………………….X

Programming is completed when 'X' is output. It takes about 2 minutes to program 512K EPROM.

builderpages/plasmo/rr512k.txt · Last modified: 2020/12/12 10:20 by plasmo
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