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.