27c16 and up

[JDTucker-5696]

Pursuant to our conversation at VCFMW, I would ask that you consider adding a 27c16 version of the code (as I believe the current RP2350 hardware already has the necessary features. Larger 27c-series chips will probably require an RP2350B, I'm thinking.). I have a current project which could benefit greatly from a 27c16-one-rom and airFrog combination. (I could also use a similar combo for use on my NABUs, but not just yet.)

I'm be keeping a sharp eye on this project, particularly the RP2350 version. My current all-time favorite RP2350 project!

[piersfinlayson]

@JDTucker-5696 Hi Jim - great to meet you at VCF MW!

I thought about this a bit further and I think the current 2316 support should also support 27c16.

See the pinout comparison - 2316 on the left, 27c16 on the right

The only difference is the 2316 CS3 pin becomes Vpp on the 27C16. Vpp should be 5V (Vcc) unless being programmed, so One ROM can consider CS3 to be active high. CS2 is /CE and CS1 is /OE. These are similarly just the same as 2316 active low lines. Hence One ROM should serve a byte if and only if CS1/CS2 are low and CS3 is high.

It should be possible to configure this type of ROM as follows:

ROM_CONFIGS=file=rom.bin,type=2316,cs1=0,cs2=0,cs3=1

I haven't tested 2316 support, as I don't have any systems which take 2316 ROMs - but it should work, as it will execute almost identical code paths as the 2332, which I have tested.

WARNING: You should verify that the equipment you plan to put you One ROM in isn't going to attempt to program One ROM as if it is a 27c16. If 25V gets applied to pin Vpp/CS3, well I expect some magic smoke would be released!

I would also double check in your equipment that Vpp is indeed always 5V (or at least, 5V when it expects to access to the ROM). I guess it's possible it's tied to GND, but the datasheet is clear it should be 5V unless programming.

Any chance you could test and let me know how you get on?

The 2332 should work similarly for 27C32 replacement - /OE (CS1) is Vpp on that IC, so CS1 and CS2 are also active low.

2364 will not work as a 27c64 replacement - as 27c64 is a 28-pin ROM. That'll need a 28-pin version of One ROM.