Reading HP67 ROMs

[Marcovecchio]

I have 2 defective HP67. The history of both machines is too long to tell here, but one of them had leaked batteries, and the other was turned on with inverted power supply, so the situation is not good.

After studying the excellent HP67 Internals document from Tony Duell, I tested all I could in the hardware, but I can't be positive about ROMs condition.

Since they're small 8 pin chips, and there are only two pins dedicated to addressing and data (ISA and DATA), I have been wondering: how do they work? What is the protocol, timings and so on? Is it documented?

What I want to do is to build a simple Arduino interfacing setup that I could use to test the ROMs. I think all I need is to read all ROM bytes, check if they're correct, and write and read all RAM positions, to assure the chips are good (or not).

Is the protocol documented somewhere? Does anyone know how these chips work?

Many thanks!