Amiga ROM Bus Driver

The Amiga ROM Bus Driver is a small sandwich module just barely larger than the Amiga EEPROM. The board has components which will act as a bus driver on the data lines with the ROM is read.

Background issue

The Amiga Romulator (an awesome product by mkstr and kipper2k) allows one to select which Kickstart ROM image to use from cold power-on. In my Amiga computers, this board was never stable. After minutes to hours of runtime, my Amiga would crash, reboot, and be stuck at a red screen. Doing a long reset or power cycling the Amiga would take it back to the Romulator menu where loading a new image would work just fine, until minutes to hours later when the cycle would repeat.

At first I suspected the SRAM onboard the Romulator was somehow being written during Amiga runtime. Measuring with an oscilloscope showed the voltage of the WE# line was only about 3V. A pull-up to 5V was done, and no glitches were seen on the oscilloscope, but this didn't cure the problem. I then added a bypass capacitor to the VCC input of the SRAM part and a larger capacitor at the 5V entrance to the Romulator. These did not make the problem go away. Finally, I wrapped the entire board in kapton tape, grounded copper tape, and more kapton tape. This also did not solve the problem.

My running theory now is that the AS6C8016 can not drive the Amiga bus with many peripherals without occasionally dropping SRAM cell bits. In order to test thistheory, I've built this sandwich module.

Intended use

Install between the Romulator and the Amiga EEPROM socket.

Board source

It is intended that this board will be open source once it has been verified to work correctly. The EasyEDA design will be made public and the Gerbers will be available in Github at that time.