First time cart making, I need some help.

[FitzGregory]

I've had almost all the equipment to make a cart at work as I am a computer tech at an electronic repair shop. All but the EPROMs. I just got my hands on a two AM27C256 EPROMs but I can't seem to figure out what pin/board modifications I need to make in order for these EPROMs to work.

When I compare the EPROM Pin outs hosted by NESdev to the pin outs on the AMD datasheet pin 27 does not match. On the NESdev chart it is address input 'A14' while the AMD datasheet shows it as the 'Program Enable Input'. Does this make this specific EPROM unusable for my pourposes?

If this EPROM is usable then I am also hitting a wall with the cartridge PCB conversion. The Dick Tracy donor cart has a 128Kbit PRG ROM. According to the NESdev ROM pinout chart the PRG ROM has Address Inputs from 0-16 while the AMD EPROM datasheet and NESdev EPROM chart show the 27C256 EPROM having only 15 Address Inputs (A0-A14). I keep reading about people using larger memory sized EPROMs, but having to fill the entire EPROM memory with the same code repeated. I must be not understanding something here as to me it looks like there are more Address Input lines in the 128Kbit Mask ROM than a 256Kbit EPROM.

[tepples]

Am27C256 is a 32Kx8 parallel UV EPROM. Its pinout matches the 32KBytes pinout seen the old doc and in the wiki page. Vpp needs to be be 12.75 V during writes. Might you have confused bits and bytes?

[FitzGregory]

Am27C256 is a 32Kx8 parallel UV EPROM. Its pinout matches the 32KBytes pinout seen the old doc and in the wiki page. Vpp needs to be be 12.75 V during writes. Might you have confused bits and bytes?

Yes. Yes I have. It seems the NESdev ROM Pinouts are organized by KBytes, not KBit. I was comparing to the wrong pin outs. Thank you for pointing that out.

This would mean my AM27C256, being a 256 Kilobit chip is too small for this cart as I need something that can hold a 128 KiloByte PRG. That would mean I need a 27C010/27C1001. Is this correct?

Edit: The 27C010/27C1001 is a 32 pin EPROM, but the Dick Tracy cart has a 28 Pin PRG ROM. Now I am confused.

Edit2: I found some long dead thread that covers this problem. Apparently there is a lot of pin bending to make things fit. Now I have to get myself some 128KiloBYTE EPROMs. Thanks for the help.

[yogi]

Am27C256 is a 32Kx8 parallel UV EPROM. Its pinout matches the 32KBytes pinout seen the old doc and in the wiki page. Vpp needs to be be 12.75 V during writes. Might you have confused bits and bytes?

Yes. Yes I have. It seems the NESdev ROM Pinouts are organized by KBytes, not KBit. I was comparing to the wrong pin outs. Thank you for pointing that out.

This would mean my AM27C256, being a 256 Kilobit chip is too small for this cart as I need something that can hold a 128 KiloByte PRG. That would mean I need a 27C010/27C1001. Is this correct?

Edit: The 27C010/27C1001 is a 32 pin EPROM, but the Dick Tracy cart has a 28 Pin PRG ROM. Now I am confused.

Edit2: I found some long dead thread that covers this problem. Apparently there is a lot of pin bending to make things fit. Now I have to get myself some 128KB EPROMs. Thanks for the help.

Nintendo used a custom 28pin 128K rom, whereas the standard 128kB roms are 32pin.
Looking at Boot Gods DB, Dick Tracy is a UNROM and the PRG footprint is only 28pin. So you could try fitting a 32pin to the board, bending the top 4 pins and use flying jumpers, or find a different UNROM donor with the 32pin footprint and do your jumpering from points on the board. Either way you will need to research the mapper logic and footprints of both the board and the EPROM you're using. You may luck out and find a how-to. RetroUSB used to offer a discrete mapper board, but seems they are dropped
Take a look at this guide for a SNROM cart, it may help give you an idea of what's involved.
http://www.54.org/sage/condev/ff2cartproject/
The main thing to look at is how the PRG rom signals are handled and re routed.
Yogi
EDIT- Found this guide that spells it out .
http://www.neswarpzone.com/tech/UNROMdev.txt
I skimmed it and looks complete. Good luck