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Using DIP28 SRAM in a DIP24 slot
http://forums.nesdev.com/viewtopic.php?f=28&t=14227
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Author:  DamienC [ Sun May 15, 2016 8:13 am ]
Post subject:  Using DIP28 SRAM in a DIP24 slot

I'm trying to repro Crisis Force using Racer Mini Yonku. I need to add a 2K SRAM chip.

The PCB has a spot for SRAM which I intend to use. I have a MB8464 DIP28 chip from another dead cart that I wouldn't mind rewiring to work in the DIP24 location, but I can't find the datasheets for either the MB8464 or the DIP24 MB8416 that actual VRC4 carts like Gradius II and Crisis Force use.

Some questions:

Can someone point me to the datasheets for these chips? I found some PDFs on Google but they're not exact matches so I don't really trust them.

Can I just use the MB8464 with some simple rewiring if the pinouts don't match?

Does it matter that the MB8464 is an 8K SRAM?

Author:  Joe [ Sun May 15, 2016 9:42 am ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

According to the wiki, these are standard SRAM chips following standard pinouts.

Lift pins 1, 2, 23, 27, and 28. Connect pin 27 to the hole under pin 23 (hole 21). Connect the other lifted pins to VCC (pin 26/hole 24).

Author:  tepples [ Sun May 15, 2016 9:43 am ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Google mb8464 datasheet and mb8416 datasheet brought me links that should be relevant. After comparing them to the page on NESdev Wiki about SRAM pinouts, and after adding the 6116's pinout that I found to be missing, I determined that the MB8464 has the same pinout as the 6264, and the MB8416 has the same pinout as the 6116.

As long as all needed enable signals are present, you can use an 8Kx8 SRAM by tying unused address lines (here, A12 and A11) to a constant voltage (either ground or +5 V). So the only signal you'll need to rewire is /WE (lift pin 23 and connect pin 27 to hole 21 under where pin 23 was), as Joe mentioned. All others (A12, A11, +CS2) can be tied to power.

Author:  Joe [ Sun May 15, 2016 9:47 am ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

I guess I looked at the wiki right after you finished editing it! :lol:

Author:  DamienC [ Sun May 15, 2016 6:28 pm ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Didn't seem to work.

I tied hole 21 to pin 27, and connected all other lifted pins (1, 2, 28, 23) to +5V. Got some garbled graphics that vaguely resemble the title screen but nothing else. I tried the same thing with another SRAM chip I had from a dead cart, a MCM60L64P12 which is an 8K chip with the same pinout. Got the same result. Not sure why it isn't working but I don't think I'm going to mess with it any further.

I ordered a 6116 from Jameco, hopefully that will work.

Author:  DamienC [ Mon May 16, 2016 2:19 pm ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Well, nuts.

I got the 6116 today and soldered it in. Still the SAME results. I was convinced at this point it was a problem with the ROM rather than hardware.

Turns out it's the translation patch from Stardust Crusaders that does something to the ROM. Loading that patched ROM with puNES produces the EXACT same graphical errors. The clean Famicom ROM works perfectly. I also didn't realize that the "translation patch" just translates the small amount of Japanese text on the title screen and rewords some of the option screen.

I have some things to do tonight but later I'll burn a few new EPROMs with the original ROM. I expect it to work.

Glad I didn't toss those other SRAM chips in the trash, they probably work. Annoyed about losing a pair of 27C010's though.

Author:  tepples [ Mon May 16, 2016 3:25 pm ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Lesson learned: Use UV or flash while learning and OTP for mass quantities once you know they work.

Author:  icemanxp300 [ Tue May 17, 2016 8:43 pm ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

It seems you already found the problem but I was going to chime in that at least from my experiences sram does not cause garbled graphics. I was going to suggest you try it w/no sram chip at all and see if it was garbled. You already figured it out though.

Author:  DamienC [ Wed May 18, 2016 3:50 am ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Actually it's still not working. When I made my last reply I wasn't at home so I assumed the correct SRAM chip would magically fix the problem (based on what I was seeing with emulators), but it didn't.

At this point I'm stumped. On power up, I get garbled graphics and can sort of navigate to the options screen and start the game. Audio is also corrupted. You can start to hear the game's music when you start the game, but then it locks up. I'll post pics of this and also the PCB maybe when I get home later today, but I'm inclined to give up on this for now.

I followed the same wiring I used for Dragon Scroll (http://forums.nesdev.com/viewtopic.php?f=28&t=14159) if that makes any difference. I checked pins 3 and 4 of the VRC chip to make sure they go to the proper location per the wiki's entry.

Author:  Ice Man [ Thu May 19, 2016 1:05 am ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Crisis Force VRC4:
(fr) CPU A3 -> |03 38| -> PRG A15 (r)
(fr) CPU A2 -> |04 37| <- CPU A12 (f)

Racer Mini Yonku VRC4:
(fr) CPU A0 -> |03 38| -> PRG A15 (r)
(fr) CPU A1 -> |04 37| <- CPU A12 (f)

(f) to Famicom only
(r) to ROM only


Make sure your wiring for these is correct, too!

Author:  DamienC [ Thu May 19, 2016 5:16 am ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Got caught up with work yesterday and didn't get a chance to hit the workbench.

I did trace out pins 3 and 4 the other day though, and they both go to the correct places on both the EPROM and the cartridge connector pins:

Code:

VRC4 Pin 3 -> PRG EPROM pin 12 -> Cartridge connector pin 13 (PRG/CPU A0)

VRC4 Pin 4 -> PRG EPROM pin 11 -> Cartridge connector pin 12 (PRG/CPU A1)



I'm also wondering about pins 16, 17 and 19 on the VRC4:

Code:
 VRC4 (f) CHR A18 <- |16  25| -> CHR A14 (r)
    VRC4 (f) /IRQ <- |17  24| -> CHR A13 (r)
                ? -- |18  23| -> CHR A11 (r)
    VRC4 WRAM /CE <- |19  22| -> CHR A16 (r)
              GND -- |20  21| -> CHR A10 (r)
                     `------'


Pin 17 is connected to /IRQ but pins 16 and 19 are not connected to anything. I tried tying pin 16 to CHR A18 on the EPROM (pin 30) but it had no effect. As for pin 19, if you look at the PCB for Crisis Force on the database, it looks like there's a resistor, a diode and a capacitor in the circuit going from pin 19 to SRAM /CE, which the Yonku PCB does not have. Could someone fill me in on what function they serve?

Author:  lidnariq [ Thu May 19, 2016 11:30 am ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

DamienC wrote:
I tried tying pin 16 to CHR A18 on the EPROM (pin 30) but it had no effect.
It's only useful to connect CHR A18 if the game had 512 KiB of CHR in the first place. (No games released by Konami did)

Quote:
As for pin 19, if you look at the PCB for Crisis Force on the database, it looks like there's a resistor, a diode and a capacitor in the circuit going from pin 19 to SRAM /CE, which the [RAMless] Yonku PCB does not [populate]. Could someone fill me in on what function they serve?
The orientation of the diode implies that that's designed to delay the fall of WRAM/CE but not delay its rise.

This is probably related to the standard annoyance where /ROMSEL is ≈20ns delayed from M2, so naïvely generating WRAM/CE as NAND4(A13,A14,M2,/ROMSEL) will produce glitches erroneously enabling the RAM on access to ROM/mapper registers in the $E000-$FFFF region.

Author:  Ice Man [ Thu May 19, 2016 12:18 pm ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

DamienC wrote:
Got caught up with work yesterday and didn't get a chance to hit the workbench.

I did trace out pins 3 and 4 the other day though, and they both go to the correct places on both the EPROM and the cartridge connector pins:

Code:

VRC4 Pin 3 -> PRG EPROM pin 12 -> Cartridge connector pin 13 (PRG/CPU A0)

VRC4 Pin 4 -> PRG EPROM pin 11 -> Cartridge connector pin 12 (PRG/CPU A1)



Those are not correct. They have to be connected to A3 and A2 like it was in Crisis Force.

Author:  DamienC [ Thu May 19, 2016 4:24 pm ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Well, I'm a dope.

I completely misinterpreted the note about pin 3 and 4 of the VRC4. For some reason I thought that since they were still tied to A0 and A1 they were fine... no clue how I got that.

I lifted pins 3 and 4 and tied them directly to the EPROM. Game works just fine now. The wires were a lot cleaner before I did all the troubleshooting:

Image

Image

Image

Author:  Fisher [ Sat Nov 18, 2017 2:27 pm ]
Post subject:  Re: Using DIP28 SRAM in a DIP24 slot

Thanks! :beer:
I was having trouble and found this thread.
Worked like a charm!
Interestingly, it became stable only after I added the diode + the resistor + the capacitor.
Perharps it's the RAM I'm using... I couldn't find it's datasheet.

Some crapy pictures from my phone:
Attachment:
File comment: Front
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20171118_191810.jpg [ 597.08 KiB | Viewed 2816 times ]

Attachment:
File comment: Solder
20171118_191826.jpg
20171118_191826.jpg [ 626.8 KiB | Viewed 2816 times ]


And some board p0rn here and here, just in case someone is interested.

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