Suggestions for FPGAs / CPLDs for custom MSX Cartridges

Master (163)

12-02-2020, 18:23

Hi all!

I'm having fun dreaming of creating custom MSX cartridges based on programmable logic. I have some experiences with FPGAs and CPLDs, but checking for programmable devices and I haven't found my "sweet spot" yet.

In particular, I'm having trouble with the fact that most FPGAs currently available are not 5V tolerant. While there are (many) techniques that can be used to link 3.3V logic to 5V logic, I'm not 100% sure of which one would give the best results.

As the "FPGA in a cartridge" is a mature topic in the MSX scene, I'd like to ask you your opinion about my options / new proposals. Right now I'm considering two possible options:

Low cost/CPLD:
MachXO (100-LQFP package)
Scales from 2$ to 15$ depending on capabilities. Needs almost no external components.

Mid cost/FPGA:
ECP5 (256 FPGA)
Scales from 13$ / device. Has lots of ram.

As the 3.3V to 5V technology to use, I am somewhat inclined to use voltage dividers (2 resistors x pin).

What would you think about those options?

thanks!

Por DamageX

Master (217)

17-02-2020, 18:15

If you have access to the Lattice design software then go for it. However, some iCE40 parts are also supported by open source tools.

Voltage dividers might be practical for a few unidirectional pins, otherwise something like a TXB0108 is probably better?

For simpler designs, old 5V Atmel CPLDs are still available (including socketable PLCC packages) ATF1504, ATF1508

Por salutte

Master (163)

17-02-2020, 21:55

Thanks for the feedback!
I do have experience programming lattice and xilinx devices, and lattice were the most comfortable to use by far.
But I am still unsure about the 3.3V /5V compatibility. I've seen that I can use the clamp diodes for this purpose too, but I'd like to know if someone has used them in practice.

Also, I'll take a look at the atf1504 and atf1508 too.