rewire help - NESdev BBS

rewire help
by coinheaven on 2010-11-09 (#69756)

so i have these 2 pinouts. trying to rewire a snes cart with a 27c512 eprom. can someone tell me what i would need to bend up and rewire?:

SNES Mask ROM Pinout:

__ __
A20 | \/ | +5V
A21 |__ __| A22
A17 |01\/32| +5V
A18 |02 31| /OE
A15 |03 30| A19
A12 |04 29| A14
A7 |05 28| A13
A6 |06 27| A8
A5 |07 26| A9
A4 |08 25| A11
A3 |09 24| A16
A2 |10 23| A10
A1 |11 22| /CE
A0 |12 21| D7
D0 |13 20| D6
D1 |14 19| D5
D2 |15 18| D4
GND |16 17| D3

EPROM 27C040/27C4001 512KBytes (32pin):

---_---
VPP - |01 32| - VCC
A16 - |02 31| - A18
A15 - |03 30| - A17
A12 - |04 29| - A14
A7 - |05 28| - A13
A6 - |06 27| - A8
A5 - |07 26| - A9
A4 - |08 25| - A11
A3 - |09 24| - OE
A2 - |10 23| - A10
A1 - |11 22| - CE
A0 - |12 21| - D7
D0 - |13 20| - D6
D1 - |14 19| - D5
D2 - |15 18| - D4
GND - |16 17| - D3
-------

by coinheaven on 2010-11-10 (#69766)

ok, i think i got most of it:

bend up pins 1,2,24,30, 31
hole 24 to pin 2
hole 31 to pin 24
hole 1 to pin 30
hole 2 to pin 31

but where would i wire A19 (hole 30) on the board to?

by koitsu on 2010-11-10 (#69783)

Topic moved to SNESdev forum.

by blargg on 2010-11-10 (#69790)

I'm curious as to why people usually recommend bending pins up. I've found it much better to cut traces on the circuit board. This way you can remove the EPROM and reprogram it easily. Cut traces are easy to reconnect if you cut the wrong one.

by tokumaru on 2010-11-10 (#69791)

blargg wrote:
I'm curious as to why people usually recommend bending pins up.

I guess it's because picking up the signals from the holes is easier than looking for other suitable solder points.

by coinheaven on 2010-11-10 (#69808)

yea i like bending up because if i cut a wrong trace the board is done. i did see that A15 can be ignored on snes boards. not sure how i would go on from there though

by jpx72 on 2010-11-10 (#69809)

this one looks like a cart-destroyer on the loose...

by tepples on 2010-11-10 (#69819)

coinheaven wrote:
i did see that A15 can be ignored on snes boards.

As I understand it, LoROM uses A15 as a positive enable and doesn't use it on the ROM itself. HiROM uses A15 OR A22 as an enable, but it does route A15 to the ROM.

by coinheaven on 2010-11-10 (#69828)

ok, so how would i wire A16-A19 on the board then?

tepples wrote:
coinheaven wrote:
i did see that A15 can be ignored on snes boards.

As I understand it, LoROM uses A15 as a positive enable and doesn't use it on the ROM itself. HiROM uses A15 OR A22 as an enable, but it does route A15 to the ROM.

by tepples on 2010-11-11 (#69838)

I've never done it before, but here's my guess: On a HiROM, pass them right through. On a LoROM, run A16-19 on the cart edge to A15-18 on the ROM.

by coinheaven on 2010-11-11 (#69841)

ok, ill give it that a shot. thanks

tepples wrote:
I've never done it before, but here's my guess: On a HiROM, pass them right through. On a LoROM, run A16-19 on the cart edge to A15-18 on the ROM.

by kyuusaku on 2010-11-11 (#69857)

That's exactly right. You don't need to use A15 as an enable either because ROMSEL is decoded with A15.