Cx4 Pinout

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qwertymodo
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Cx4 Pinout

Post by qwertymodo » Thu Jul 18, 2013 12:40 am

I can't seem to find a pinout of the Cx4 coprocessor, so I've traced it out for myself. I have 78 of the 80 pins traced, and the other 2 are probably inputs, which are a lot trickier to figure out than outputs. Maybe one is a Hi/LoROM signal like MAD-1 pin #10?

A0..23, D0..7, RD, WR, RST, etc. are connected to the cart edge
RA0..20, RD0..7, ROE, RCE, etc. are connected to the ROM
RCE1 is CE on the first ROM if 2x8Mbit ROMs are used, or the only ROM if a 16Mbit ROM is used
RCE2 is CE on the second ROM if 2x8Mbit ROMs are used
SCE is SRAM /CE

Code: Select all

1   A3     21  A15    41  RA8    61  /IRQ
2   A4     22  A14    42  RA7    62  D7
3   A5     23  A13    43  RA6    63  D6
4   A6     24  A12    44  RA5    64  D5
5   A7     25  /SCE   45  RA4    65  D4
6   A8     26  /RCE2  46  RA3    66  Vcc
7   A9     27  /RCE1  47  RA2    67  D3
8   A10    28  RA19   48  RA1    68  D2
9   A11    29  RA18   49  RA0    69  D1
10  GND    30  RA17   50  GND    70  D0
11  XIN    31  Vcc    51  /RWE   71  Vcc
12  XOUT   32  RA16   52  /ROE   72  /RST
13  A23    33  RA15   53  RD7    73  GND
14  A22    34  RA20   54  RD6    74  ???
15  A21    35  RA14   55  RD5    75  ???
16  A20    36  RA13   56  RD4    76  /RD
17  A19    37  RA12   57  RD3    77  /WR
18  A18    38  RA11   58  RD2    78  A0
19  A17    39  RA10   59  RD1    79  A1
20  A16    40  RA9    60  RD0    80  A2
Pins 73-75 are a bit weird, the fact that they're all GND, and on MMX2, there's what appears to be an optional jumper between pin 75 and the other two. So they may have a purpose on the chip, but they aren't used on either MMX2 or MMX3.

Edit: I've removed the chip from the PCB, and pins 74 and 75 are NOT internally connected to GND, so they are obviously not supply ground pins, they're probably inputs, but possibly I/O, and just tied to ground on the PCB. I've changed them in the pinout list.

Edit 2: Pin 61 is /IRQ. Somehow missed that one during continuity testing.

Edit 3: Despite what I said about /RCE1 being used as the only ROM /CE for a single-ROM board, Nintendo apparently decided instead to use /ROE as a /CE signal on RMX3/MMX3, and the ROM chip's /OE pin is just connected to Gnd. Nonetheless, I can confirm that /RCE1 can be used as a /CE signal for a single ROM board, if /ROE is used for its intended purpose and connected to the ROM's /OE pin.

If anybody has any more information, I'd really appreciate it.
Last edited by qwertymodo on Fri Dec 20, 2013 11:43 pm, edited 6 times in total.

nocash
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Re: Cx4 Pinout

Post by nocash » Sat Jul 20, 2013 4:48 pm

Gazing at the PCB photo, pin 73+74 seem to be wired straight to GND, so they are probably normal supply GND. If you really wanted to, you could lift the pins, and check if they are interconnected inside of the chip. If they aren't, then one of them may be something special.

And pin 75, looks as if one is supposed to cut the CL link, and to install the R4 resistor instead (which probably pulls pin 75 to VCC?). If you've some tool for dumping the cartridge, you could do some before/after test... maybe it maps it as HiROM instead of LoROM... or it makes the game 500 times faster :-)

For the two ??? pins, maybe SRAM select, and SRAM write? Since they are near ROM selects and ROM read accordingly.

byuu
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Re: Cx4 Pinout

Post by byuu » Sun Jul 21, 2013 4:49 am

Ah yes, if I haven't mentioned it ...

The Cx4 maps 70-77:0000-7fff to SRAM. It always reads as 0x00 (not open bus) on MMX2/MMX3.

Seems Capcom had intended to allow the chip to optionally support SRAM at some point, but of course it never ended up being used.

qwertymodo
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Re: Cx4 Pinout

Post by qwertymodo » Mon Jul 22, 2013 12:44 am

byuu, just thought I'd point out that pin 34 is not /WE like Charles MacDonald seemed to think. At least, I can confirm on MMX3, it's connected to ROM A20. So, I'm not sure if programming the ROM via the cart edge is even possible. I'm still figuring out the various quirks of my logic analyzer, but I'll try to figure out those last 2 pins. The assumption that they're SRAM control lines at least gives me something to go on. If it turns out that it's not possible to perform writes to ROM, but we can figure out the SRAM control signals, would it maybe be feasible to wire in an SRAM module, burn a simple ROM that bootstraps to SRAM, then you could upload your code to the SRAM and run your tests that way?

byuu
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Re: Cx4 Pinout

Post by byuu » Mon Jul 22, 2013 1:25 am

Would it not be easier to tap /WE right off of the connector pins at the bottom of the PCB?

I am not sure how easy it'd be to rig up SRAM onto the board, and be able to write into that SRAM otherwise. But ... yes, I can do any reads and/or writes after the cart is inserted to get code onto the Cx4 to execute.

I believe both nocash and Overload have successfully made their own Cx4 proto boards, so we might ask them for advice?

Overload's board:
Image

My guess is they were probably able to just reprogram the flash ROM directly, which isn't something I can easily do.

qwertymodo
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Re: Cx4 Pinout

Post by qwertymodo » Mon Jul 22, 2013 4:14 am

Is that second board another SNES cart? Why?? :shock:

And yes, it would be possible to just tie the ROM /WE directly to the cart /WE, I'll just have to do some tests to ensure that the data bus is active during writes to the ROM address space.

As for the SRAM, 70-77:0000-7FFF gives 480KBytes addressable, right? I know that's kind of a dumb question, but it's late, and I don't trust my sleep-deprived math skills...

nocash
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Re: Cx4 Pinout

Post by nocash » Mon Jul 22, 2013 5:52 am

qwertymodo wrote:Is that second board another SNES cart? Why??
I think that design isn't mandatory :-) maybe overload did have some un-socketed SRAM/FLASH memory on the left board, and decided to hook it up to the CX4 board.
A smaller daughterboard with memory chip socket should do it, too. Myself, I would probably use ribbon cables to wire it to the CX4 ROM pins (and keep CX4 ROM installed, only deactivate it's /CE pin).
Byuu, no, I don't have any CX4 hardware.
qwertymodo wrote:And yes, it would be possible to just tie the ROM /WE directly to the cart /WE, I'll just have to do some tests to ensure that the data bus is active during writes to the ROM address space.
Ideally, you would full write access to ROM (via RD0..RD7 databus, and CX4 Pin51=/WE (or alternatly, less ideal, via SNES cart /WE)). Might be a 50% chance that Capcom has implemented it like that.

If the databus is inactive during ROM writes would be a problem. But there should be a way around that: You could have /ROMCE1 (CX4.Pin26) ANDed with /SRAMCE (CX4.Pin25, presumably), and wire that to you FLASH/SRAM chip. Then you'd have full write access (to banks 70-77), and would get the same memory mirrored to ROM area (banks 00-07). That should work fine (unless you need more than 8 banks).
qwertymodo wrote:As for the SRAM, 70-77:0000-7FFF gives 480KBytes addressable, right?
Could be also 256Kbytes (8 x 32K)... but not sure, I just woke up and didn't had much coffee yet.

PS. no idea what CX4 Pin 61 could be intended for (if it does have any purpose at all).
Last edited by nocash on Thu Jul 25, 2013 4:51 pm, edited 1 time in total.

qwertymodo
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Re: Cx4 Pinout

Post by qwertymodo » Mon Jul 22, 2013 5:34 pm

nocash wrote:
qwertymodo wrote:As for the SRAM, 70-77:0000-7FFF gives 480KBytes addressable, right?
Could be also 256Kbytes (8 x 32K)... but not sure, I just woke up and didn't had much coffee yet.
That sounds better... not sure where I came up with 480 -_-

Overload
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Re: Cx4 Pinout

Post by Overload » Thu Jul 25, 2013 2:59 am

qwertymodo wrote:Is that second board another SNES cart? Why?? :shock:
Yes, the second board is another snes board with the maskrom removed replaced with a socket. Flashrom is socketed on the second board and the wires match pins with the second maskrom of a Rockman X2 board which has also been removed. Used to run custom code on the CX4. :D

qwertymodo
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Re: Cx4 Pinout

Post by qwertymodo » Fri Jul 26, 2013 4:15 pm

Overload wrote:
qwertymodo wrote:Is that second board another SNES cart? Why?? :shock:
Yes, the second board is another snes board with the maskrom removed replaced with a socket. Flashrom is socketed on the second board and the wires match pins with the second maskrom of a Rockman X2 board which has also been removed. Used to run custom code on the CX4. :D
Why didn't you just wire a socket to the MMX PCB? :P

byuu
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Re: Cx4 Pinout

Post by byuu » Fri Jul 26, 2013 11:01 pm

My guess would be pin sizes not accommodating the socket. The Cx4 ROMs are tiny.

qwertymodo
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Re: Cx4 Pinout

Post by qwertymodo » Sat Jul 27, 2013 12:57 pm

byuu wrote:My guess would be pin sizes not accommodating the socket. The Cx4 ROMs are tiny.
It's not that bad

No big deal, though. To each his own :)

qwertymodo
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Re: Cx4 Pinout

Post by qwertymodo » Sun Aug 04, 2013 3:06 pm

I've removed the chip from the board, and pin 73 is supply ground, pins 74 and 75 are not. I updated the list above to reflect that. So that leaves me with 5 unknown pins.

nocash, if you used my info in your docs, you should probably change that.

qwertymodo
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Re: Cx4 Pinout

Post by qwertymodo » Mon Aug 12, 2013 9:05 pm

Pin 61 is /IRQ. It connects right up to the cart edge. Not sure how I missed it. Derp :P

nocash
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Re: Cx4 Pinout

Post by nocash » Tue Aug 13, 2013 2:24 pm

The CX4 supports IRQs? Cool. That's new to me.
As far as I know the megaman games don't use that feature.
At least they seem to work without emulating it.

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