Stacking 4x27c801 to build a 32Mbit cart.

I had so much fun building my first snes repo cart ( Zelda Parallel worlds ) that I want to try something harder. I want to build an NTSC patched Terranigma cart. I sorted through my collection and found a cart that I'd be willing to sacrifice for the challenge and confirmed that both Terranigma and Donor match.

Target -> Terranigma: 64K SRAM, Hirom, 32Mbit, Fastrom
Donor -> Ken Griffy Jr Winning Run: 64K SRAM, Hirom, 32Mbit, Fastrom

Some immediate confusion though, Ken Griffy uses a single 36pin 32Mbit eprom. For the challenge I want to use 4x27c801 eproms which are of course 32pin 8mbit eproms. I do not want to try the 40pin TSOP to 36pin dip method yet... I'll save that for my third challenge

Previously when using 2x27c801 on a cart that already had (2) 32pin slots it was simply a matter of building and splitting the rom correctly and then rerouting the 2 addresses on each of the 27c801 eproms. I'm unsure how to properly stack 4x27c801 chips together and then how to properly wire the stack to the single 36pin slot. I assume that I'll also have to wire each of the 27c801's into the existing "MAD-1 A" chip thats already on the donor cart.

Any help or direction would be sincerely appreciated.

Thank you!

MAD-1 natively supports connecting one or two ROMs only. If you're using four, you'll need extra hardware (a 74'139 or 74'138)

@lidnariq - Thank you for reply, it was actually quite helpful. Your tip on the *39 chips cleared up Kogami's diagram for me.

Don't do it! 27C801s are so expensive these days. Use some other memory chip. It's also a pain to fit all those chips into the casing afterwards.

@Motzilla - I hear ya, I was going to go to order some "AM29F032B-90EC -TSOP Adapter III" from buyicnow, but they've been sold out...

One question that I haven't been able to find an answer to is, if I purchase the AM29F032B-90EC already mounted on the TSOP Adapter 3, do I need to use an adapter to program it on a Willem GQ-4X ?

What device profile would I associate the TSOP adapter 3 with ?

If anyone knows the answer to this, it would save me another night of scouring the mcumall forums.

Thank you!

hello friend, here is the solution to your problem



regards

@skarstoker - THANK YOU! This is perfect!

Looks like buyicnow has some stock, am I correct in thinking that the "ST M29F032D-70N6 (TSOP Adapter III)" pre-mounted solution is compatible? I see that many people are using AM29F032B-90EC. Is speed the only difference between the two chips ? If I understand correctly, the only difference between the 70N6 and the 90EC is the speed, 70N6 being faster and more expensive, though noting that the snes won't benefit from anything faster than "120" ?

Still learning, but having a lot of fun. Thank you all for your help.

Since BuyIcNow is always out of stock, I've gone ahead and built a test bread board with zif sockets using 2x27c801's and 74LS139 wired up to an IDE connector based on Kogami's 4 eprom diagram. I'm trying to build a 16Mbit HIROM test board. I'm a bit confused though about the address remapping.

The diagram says to route A18 and A17 to the locations market A18 and A17 on the PCB. However it does not say where to route the pins that would normally populate those same locations on the PCB, A15 and A12 on the 27c801. Are these supposed to float or do they get remapped on the board too ?

Have you tried it...? Because I'm about to make a cart similar to Kogami too !
Did you make the wiring according to the swapbin method or like on the picture??
Thanks

For 2x27c801 you do not need the decoder 74LS139, you need the presence of MAD-1 on donor.

I'm gonna go for 4 27c801 on my test cart...personal challenge (+Flash 29f032).
I wanted to learn a bit more about those types of mounting. (Sandwich 4 eproms).

To save one cable I was thinking of using the /OE on pin 33 of maskrom instead of pin 4 of Mad-1.
Kogami, is there a lot of cables under you test cart or is it all tin bridges?

You could check out this post...

viewtopic.php?f=12&t=10759#p122138

I have been where you are now..... except I made a pcb that does all the wiring for you.
I don't really use this anymore and I have extras.

But to answer your question, you can't use more than 2 EPROMs on a mad1 cart. The 74xx139 is your best choice. Not too many threads down, I posted a schematic of how to wires the roms to the 139...


viewtopic.php?f=12&t=10880#p123783

Think about this.... Each address line doubles the rom size. So 27c080 EPROMs have up to address 19 (A19). So the next 27c080 would be A20 (2x 27c080 = 16mbits or 2 mBytes)
Since A20 is 16mbits, then A21 would be double the 16mbits to equal 32mbits. So the 74xx139 decodes which 27c080 gets chosen by the A20 and A21 address lines. Only 1 roms can be active at a time otherwise you would have bus conflicts. That's what the 139 does. So the OE (mad1 pin 4 which is exactly the same as the Rom OE) enables the decoder or not, depending if the OE is driven high or low.

So with this in mind, if you wanted to use 8 x 27c512 EPROMs. Then you'd need to use the decoder 74ls138 using the A19,A20, and A 21 to do the decoding of which of the 8 roms are chosen. Now I don't know WHY anyone would want to use 8 27c512 EPROMs outside of academic purposes but maybe it helps in your understanding.

So the tsop adapter is a 32mbit device which already has addresses A20 and A21 so no decoder needed.

The swap bin is useful only to reduce the amount of wiring or re-wiring of the the EPROMs to match the carts mask rom pinouts. It won't help you in how many EPROMs you'll use.

Thanks Mark,
Your summary of the decoder is very clear and it confirms what I had in mind.
I saw your adapter on youtube (possible?) and it's a good idea but since it's only for a test cart I'm gonna
wire it the old way.
My goal was to avoid opening my console each time I wanted to test a mod so my Test Cart is gonna link my SHVC-1J3m with
a IDE cable ...that way the cartridge will fit the snes console slot.
Feedback comming soon!
Peccost

Glad to help. Soooooo many fantastic people here helped me so I'm glad I can give back.

Since you are making this test cart, then you should add 1 more option to it. Pin 35 of the mask rom (hi rom) would be the next address. This is where you get the "extended hi rom".

viewtopic.php?f=12&t=10805#p123850

I haven't quite thought this through, but off the cuff, I suspect a 74xx138 would give you access to up to 8 27c080 EPROMs.... But the ExHirom are usually only 6mbytes or 6 27c080 EPROMs

So the 138 would use A20, A21, and A22 (pin 35 mask rom) as inputs.

Or you could add a second 139 decoder (or use the other half of the one you'd be using) for A22.
Just thinking out loud there......

Happy tinkering!

If so I would probably go with the second decoder of the LS139. (If I have enough space)
Thanks for the tip, but is there a Roms of 8 Mbytes?

The 27c080 is 8mbits, 1 mbyte.

If you want to use DIP EPROMs, the 27c080 is the biggest EPROM in a 32 pin package.
There is a larger dip eprom that is 42 pins 27c016 (16mbits or 2mbytes) that can be used.
The 27c016 can be configured through the byte pin to be 8 bit or 16 bit. 16 bit just means it has double the output data lines and all you need/want is 8 bit. This chip has a "byte" pin for this purpose.

Your only other option is a 27c322 42 pins EPROM. It's 32mbits and 16 bit only. The reason why it 16 bit only if because it had to use the byte pin as an address line. There are only so many pins available and they sacrificed the byte pin to add the extra address line A20. Now you might be thinking, wait a minute..... On the other chips, we talked about A21 being the 32mbit address line. True.
But when you have 16 bits, it's smaller than 8 bit but still the same. Wrap your mind around this...
16bit chip x 2mbytes = 32mbits. Highest address is A20
8bit chip x 4mbytes = 32 mbits. Highest address is A21

The 27c322 can be used with data converters discussed in a forum here not too long ago -- I'll post a link later... But essentially, with a few multiplexer chips, if converts the 16 bit EPROM into 8 bit.

Edit:

viewtopic.php?f=12&t=4877&start=45#p124330

I've seen all this stuff in school but I forgot all of it and I'd like to master it once for all.
Thanks again for your help

p.s. Still, I thought the biggest Snes game was Tales of Phantasia 6Mb?

I don't know of any bigger games than 6mB (Tales of Phantasia).

There's 48 Mbit (ToP), and then there's 48 Mbit that's packed so tightly it takes a coprocessor to unpack it (Star Ocean, Street Fighter Alpha 2). The lookup tables inside the coprocessor aren't part of the ROM image as commonly understood, but they are on a component soldered to the PCB that contains ROM.

True. I think he was just referring to games that were on a standard HiRom cart.