SRAM decoder 74LS139 for 27C160/27C322 LoRom/HiRom

[Kayumba]

Hi everyone,

I trie to do my first 27C160/27C322 LoRom/HiRom cartridge PCB with SRAM.
I'am confuse with this table on this picture for SRAM decoder 74LS139 MaskRom pin 31
Can you tell me if I do right connections, please.

https://thepoorstudenthobbyist.com/2019 ... ter-board/

On my 27C322 maskrom, pin 31 is GND


And when I look to this picture, pin 31 is Q15(=D15)

[lidnariq]

27C322 maskrom

"mask" ROM means something. A 27C322 is not a "mask" ROM. Instead, it is an UltraViolet-Erasable Programmable ROM.

Different ICs put different functions on different pins. Compare, for example, the pinout of the SST39SF040 (A18 on pin 1, /WR on pin 31) to that of the AM27C040 (A18 on pin 31, Vpp on pin 1). You can't just use pin numbers; you have to look at what the meaning of the signal is for each pin and handle it accordingly.

Even among very closely related parts (for example, a 28-pin 27C512 compared to a 32-pin 27C010) pin numbers aren't consistent.

[Kayumba]

27C322 maskrom

"mask" ROM means something. A 27C322 is not a "mask" ROM. Instead, it is an UltraViolet-Erasable Programmable ROM.

Different ICs put different functions on different pins. Compare, for example, the pinout of the SST39SF040 (A18 on pin 1, /WR on pin 31) to that of the AM27C040 (A18 on pin 31, Vpp on pin 1). You can't just use pin numbers; you have to look at what the meaning of the signal is for each pin and handle it accordingly.

Even among very closely related parts (for example, a 28-pin 27C512 compared to a 32-pin 27C010) pin numbers aren't consistent.

Yes, here also its that word "Mask Rom"...that confuse me
I know that 27C322 its an EPROM.
But when it's says "Cartridge PIN number" 31 and when I see that on cartridge there is NO pin 31.
Its begin from pin 5->27 and 36->58
And that function of pin name /OE (/CART) we found on SNES cartridge PIN number 49.
Is it right?

[poorstudenthobbyist]

In that table, Mask ROM pin 31 is the 31st pin on the original cartridge ROM socket. The "Mask ROM" is the original ROM chip that is installed on the board.

Look at the middle picture for what I'm referencing.

[Kayumba]

When eprom 27c322 are programmed with ROM file.
Where Will be adress of /OE ? In what pin number?
Do the signal adresse changes after ?



If i understand right,
All i have to do is to know where in my 27c333 the adress of /OE, yes?
If its right, so its have to be pin 13 of 27c322.
So i have to connect 74LS139 pin 7 (1Y3) to pin 13 of 27c322

[Kayumba]

When eprom 27c322 are programmed with ROM file.
Where Will be adress of /OE ? In what pin number?
Do the signal adresse changes after ?



If i understand right,
All i have to do is to know where in my 27c333 the adress of /OE, yes?
If its right, so its have to be pin 13 (/G VPP) of 27c322. Exactly same like in 27C160.
So i have just to connect 74LS139 pin 7 (1Y3) to pin 13 of 27c322
Is that right?

[poorstudenthobbyist]

Not exactly. The 16 bit databus of the '322 needs to be changed to an 8 bit databus, if you recall from another thread I believe you asked about.

The way I do it is /OE connected to GND on the 322 so it always makes the 16 bit output to the multiplexers when selected by /CS. Then, the /OE from the SNES is connected to the /OE of the multiplexers to control the 8 bit data output.

/OE on the SNES cartridge is connected differently based on Hi or LoROM. There are multiple ways to connect them ultimately but I used the way the SNES carts were originally wired. Look at this page for a better explanation instead: https://thepoorstudenthobbyist.com/2019 ... planation/

[Kayumba]

The way I do it is /OE connected to GND on the 322 so it always makes the 16 bit output to the multiplexers when selected by /CS. Then, the /OE from the SNES is connected to the /OE of the multiplexers to control the 8 bit data output.

Like here?


By the way, this schematic will work ?
Can I use this schematic to try ? Or there is some mistakes?
I take it from post of LittleRain user http://forums.nesdev.com/memberlist.ph ... ile&u=9386
here:
http://forums.nesdev.com/viewtopic.php?f=28&t=19395

[poorstudenthobbyist]

The way his multiplexers are wired is indeed what I was talking about.

It looks like his schematic is for LoROM only. I can't verify it'll all work but it looks ok at a quick glance. All the information for the connections are on the site I linked though.

(I spent a lot of time writing it )

[Kayumba]

The way his multiplexers are wired is indeed what I was talking about.

It looks like his schematic is for LoROM only. I can't verify it'll all work but it looks ok at a quick glance. All the information for the connections are on the site I linked though.

(I spent a lot of time writing it )

Thank you.
Will try to take a time to learn and do something the same.
I'll better to solder some many, many wires to test it before to order PCB...