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

[dmh]

Just curious if anyone has attempted or successfully built the Casio fx-702p expansion memory module that there was a slot for but Casio never released?

Wondering how difficult it would be or if it just needs a memory chip wired to an appropriate connector.

The 702p has such limited memory that an expansion module would be useful.

[blackjetrock]

(06-13-2023 11:49 AM)dmh Wrote:  Just curious if anyone has attempted or successfully built the Casio fx-702p expansion memory module that there was a slot for but Casio never released?

Wondering how difficult it would be or if it just needs a memory chip wired to an appropriate connector.

The 702p has such limited memory that an expansion module would be useful.

If you look at the service manual schematic it is labelled as a ROM PCB, and someone found a ROM keyword in the code, apparently.
The pinout is there as well, but the instruction set isn't known as far as I'm aware, so what you'd put in the ROM is difficult to say. The pinout suggests some form of Casio 4 bit bus like on the 502P and 602P family.

Andrew

[dmh]

Thanks.

The following mentions 4Kb and 8Kb RAM modules (unreleased) so I assumed it was for RAM not ROM.

http://www.datamath.org/Related/Casio/fx-702P.htm

(06-13-2023 12:25 PM)blackjetrock Wrote:  

(06-13-2023 11:49 AM)dmh Wrote:  Just curious if anyone has attempted or successfully built the Casio fx-702p expansion memory module that there was a slot for but Casio never released?

Wondering how difficult it would be or if it just needs a memory chip wired to an appropriate connector.

The 702p has such limited memory that an expansion module would be useful.

If you look at the service manual schematic it is labelled as a ROM PCB, and someone found a ROM keyword in the code, apparently.
The pinout is there as well, but the instruction set isn't known as far as I'm aware, so what you'd put in the ROM is difficult to say. The pinout suggests some form of Casio 4 bit bus like on the 502P and 602P family.

Andrew

[blackjetrock]

I think as the schematic mentions ROM that it is probably ROM, but I suppose RAM would also work with appropriate code driving the module. I have thought about building a module for the FX702P but i don't actually have a working unit out of several that I have bought so I couldn't test it. Then there's the problem of what to put in it if it is a ROM...

Andrew

[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.