Can it be done? save RAM inside TE?

[thesteve]

well yes, but that could be a flash chip in itself
simply having the unlock address programmed into a rom
say a 29f800 with all its data low except the unlock address 1 bit high and the access range a different bit high
that would cover the address decoding, then you would just need an 8 input 1 output gal for the unlock data
add another input or a nor gate and it becomes latching

[wilykat]

Someone's going to have to get what's left of NEC to cough up the original datasheet for HuC2601 or any useful details. Otherwise someone will have to dump the chip somehow.

I don't know how it's supposed to work and I have no idea if SRAM can have the data connected directly to the bus or not.  It is possible that HuC6201 has to be the one with data access.

A shitload of data sniffer and feeding address one at a time until you see something and see what it does and how it works.  If the data into HuC6201 and data out to SRAM are the same, then that can save a few pins on replacement CPLD. If they are different for some reason, then no.

[TheOldMan]

well yes, but that could be a flash chip in itself
simply having the unlock address programmed into a rom

Didn't think of that. So you could use a chip to detect the $7f (io page) part of the address, and use that output to turn the chip on so the programmed data would appear on the data lines?
Maybe. The BRAM unlock is different register on a read, though, iirc.

I think you could do it, just don't think it would be as simple as it appears.
Just to satisy my curiosity, could you put an 8 bit A-B switch in a small programmable device? If so, it might make things easier...(Switch between BRAM and regular memory based via the switch)

[thesteve]

dont know about that, but it woundnt be needed
you just enable the chip you want to access

[wilykat]

In the meanwhile after making a custom pad for HuC6201, it seems no one made a 13x19 SOIC pad that I can use.  I have made a quick test board to see if all could fit:



Red area are the controller PCB supports (rough approximate, a 12" long (30cm) caliper that's over 30 years old is not made for measuring small space), there is room for the whole thing but I may need to hack and split that 38 pin connector (solder on ribbon cable) into 2x 19 and offset it so the cable wouldn't get pinched somewhere between the new board and the cart connector end.

I am still playing with part positioning and traces to see what can work

[thesteve]

just a note
on the TE/GT the motherboard is the same, only the cart slot board is wired different

[wilykat]

I updated the board with a few support that I omitted from the original measurement and despite my best effort I can get all but one wire done. I may have to use jumper.  I had to remove the 4 jumper pads and the LED to reduce the number of incomplete connection, I could use jumper and clip anyway for checking LED.

https://www.dropbox.com/s/ub86szklfjpw1mk/Psx.zip?dl=0

If you're experienced with Eagle and want to try playing with the component placement or wiring.

[wilykat]

I think I got it. I changed the 3 caps to be SMD and I was able to make it complete.  Shrunk the PCB by removing empty spaces and I'll get it sent off to OSHPark to see if the board works and fits as I hope.