has anyone built the unreleased Casio fx-702p memory expansion module?

[Jeff_Birt]

I suspect the 4-bit ROM protocol will be similar to the 4-bit RAM. I have been playing with using a PIC chip to emulate the 4-bit RAM. It works for the most part, there are a few edge cases that need to be ironed out though. I have not worked on it for months, got distracted with other projects.

Based on how the RAM works at power on/reset the main ROM will poll to detect if a RAM (ROM) is present. For the RAM a reset and power cycle do different but similar things w.r.t. RAM module detection. Would guess for ROM it is similar, i.e. reset will set the system up to use the ROM and at power on it will make sure ROM is still there.

Project link:
https://github.com/Jeff-Birt/Casio_PICRAM

This was based on the excellent work of Piotr:
http://pisi.com.pl/piotr433/hardware.htm...%204-bits.