This is a RAM diagnostics for the Epson PX8 (and probably PX4) portable computers.
A RAM fault can give the appearance that the PX8 is completely dead.
I do not know who the author of this test ROM is, I obtained it from this excellent website here RAMTEST.zip
Unfortunately it comes with next to no instructions!
To figure out how it works I trawled through the disassembly and cross referenced with the PX8 technical manual to come up with the annotated disassembly in this repo. It may not be 100% but was good enough for what I needed.
Early on it looks like a test is performed to determine whether the machine is a PX8 or PX4. I only analysed the PX8 path but presumably it will work in the same manner on a PX4.
- Write the binary to EPROM.
- Install in place of the OS ROM (under the small hatch on the bottom).
- Attach a terminal connection between the PX-8 RS232C connector and your terminal host computer.
- Configure terminal; 4800 baud, 8 data bits, odd parity, 2 stop bits
- Power on the PX8.
- Press the PX8 Initial Reset switch (in the ROM compartment).
The result of the memory test is output to the attached terminal;
- A bit field showing in which bits errors have been detected (X=error, .=ok)
- A list of the RAM ICs (as labeled on the PCB silk screen) that are associated with the erroneous bits.
Here's an example identifying 6 bad chips on one of my PX8 (using the terminal app on an NC100);
The test ROM checks the RS232C DSR signal before transmitting any data, so make sure that your cable includes this signal (or at least asserts it).