agkaminski / emuprom

DIY 27C256 EPROM emulator

emuprom

DIY ATmega8 based 27C256 EPROM emulator. Human accessible UART interface (19200N1, CH340 on USB C).

Revision D has been verified and it is working as intended (working both with TL866 EPROM programer and FellaPC computer).

Target connection

Via ribbon cable with DIP-28 adapter. Uses 40 pin IDC connector, but only 28 pins are used. Target power state detection is supported (external bus is resistant to the target high-z bus state).

Crude cable schematic, top view (should be enough to be able to make this cable):

Sanity check - EPROM GND (pin #14) should be on the one before last wire (bottom of the picture).

UART interface

Available via USB C UART port, 19200 baud, no parity, 1 stop bit. Interface is human friendly, but also easy to script. Available commands:

• ? - help
• ! - claim bus, memory edit, assert /RST
• . - release bus, deassert /RST
• @ - set address mode
• # - set data mode
• = - dump 256 bytes @addres
• t - memory test
• + - echo on
• - echo off
• m - calculate md5 sum
• s - clear memory (all 0xff)
• r - reset target (pulse /RST)

Example sequence with comments:

• - echo disable,
• ! - claims the bus,
• @0000 - sets address to zero,
• # - selects data mode,
• 0102030405060708 - 8 bytes are written at address 0,
• . - release the bus and start the target,
• + - enable echo.

Or all at once: -!@0000#0102030405060708.+

Uploading FW

avr-gcc, avr-libc and avrdude are needed.

• make (build FW),
• make fuse (set fuses to set internal RC @8MHz),
• make install (upload FW).

Pictures

This is a picture of revision D. Note the recommended heat shrink sleeve, to prevent accidental short circuits.