boards with 2 mask roms + 2 27c040 = 1MB?

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Bernkastel_Kues
Posts: 20
Joined: Mon Jun 15, 2015 8:43 pm

boards with 2 mask roms + 2 27c040 = 1MB?

Post by Bernkastel_Kues » Sat Dec 12, 2015 6:47 pm

can you use one of those snes boards with two mask roms to use two 27c040 to create a 1MB repro? I know people would usually use them to make a 2MB with two 27c801 but I have none of those and many 040

if you can, how would I split the rom?

zzattack
Posts: 14
Joined: Wed Oct 21, 2015 4:26 pm

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by zzattack » Sat May 14, 2016 6:36 pm

Not easily, you'd have to modify the decoder so that it enables ROM2 past >512kB into the ROM instead of 1MB (so at A19 instead of A20). That alone would be tricker than just getting a 27c080 or a eeprom adapter board.

lidnariq
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Location: Seattle

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by lidnariq » Sat May 14, 2016 6:55 pm

Rewiring a small DIP IC is no harder than rewiring for a ROM.

If a board with a MAD-n instead of a 74'139 or 74'00 .... you'll need this.

MaskRomz
Posts: 7
Joined: Sat Dec 21, 2019 9:24 am

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by MaskRomz » Sat Dec 21, 2019 11:11 am

"can you use one of those snes boards with two mask roms to use two 27c040 to create a 1MB repro? I know people would usually use them to make a 2MB with two 27c801 but I have none of those and many 040"
I have the same problem here, and I need some kind of schematics to rewiring the 74ls00 to use two 27c040 or 39sf040 to create 1mb game, Anyone can help? :roll:

lidnariq
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Location: Seattle

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by lidnariq » Sat Dec 21, 2019 1:11 pm

Nintendo used the "YA0N" and "YJ0N" board names for PCBs that used two 4 megabit ROMs and no save RAM.
YA0N:

Code: Select all

            /¯|
           / 0|o- /ROM1CE
SNESA20 --|   |
           \ 1|o- /ROM2CE
            \_|
             o
/ROMSEL -----+
YJ0N

Code: Select all

            /¯|
           / 0|o- /ROM1CE
SNESA19 --|   |
           \ 1|o- /ROM2CE
            \_|
             o
/ROMSEL -----+
Either way, the pictured demultiplexer is a 74'1g19, 74'138, 74'139, 74'00, whatever.

MaskRomz
Posts: 7
Joined: Sat Dec 21, 2019 9:24 am

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by MaskRomz » Sat Dec 21, 2019 1:41 pm

Thanks for the fast answer my friend, thats was exact whtat i searching for. So the YA0N pcb is for two 4mb eproms but i have 2A0n-10, its possible rewire the 74ls00 to make two 4mb eproms work on this board? or I need to use only YA0N?

lidnariq
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Location: Seattle

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by lidnariq » Sat Dec 21, 2019 1:46 pm

2A0N is the same as YA0N except that it uses a different address line. (YA0N uses A20 because the ROMs are connected to A0-A14 & A16-A19; a larger ROM will be connected to more address lines so the demultiplexer must be connected to a different one)

MaskRomz
Posts: 7
Joined: Sat Dec 21, 2019 9:24 am

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by MaskRomz » Sat Dec 21, 2019 2:01 pm

I split an 8mb game(legend of zelda) into two 4mb eproms and put them on the 2A0N board but does'nt work, works only with 4mb games in just one eprom (left the other eprom slot empty) and the address line used on 74ls00 is A20 like on the YA0N

lidnariq
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Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by lidnariq » Sat Dec 21, 2019 2:32 pm

aLttP has RAM, I wouldn't assume it would work without it.

MaskRomz
Posts: 7
Joined: Sat Dec 21, 2019 9:24 am

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by MaskRomz » Sat Dec 21, 2019 2:39 pm

Ofcourse! but i tried with top gear 2 too and don't work as well. but, sorry my noob question, the 4 mb eproms don't have the A19 address, and you said A16 to A19 and A0 to A14 right? so there is not A15 used? or it is omitted to use A18 as "A19"?

lidnariq
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Location: Seattle

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by lidnariq » Sat Dec 21, 2019 2:40 pm

SNESA15 isn't used on the [12Y]A0N boards. SNESA16 through SNESA19 connect to ROMA15 through ROMA18.

MaskRomz
Posts: 7
Joined: Sat Dec 21, 2019 9:24 am

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by MaskRomz » Sat Dec 21, 2019 2:52 pm

So i let the snesA15 empty and put eprom A15 in snesA16 and so on until A19?

lidnariq
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Location: Seattle

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by lidnariq » Sat Dec 21, 2019 3:05 pm

Yes, and that's how the 2A0N board you are modifying should have already been.

MaskRomz
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Joined: Sat Dec 21, 2019 9:24 am

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by MaskRomz » Sat Dec 21, 2019 3:14 pm

the same on the two Eproms?

lidnariq
Posts: 8940
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: boards with 2 mask roms + 2 27c040 = 1MB?

Post by lidnariq » Sat Dec 21, 2019 3:49 pm

Other than the different /CE (or maybe /OE) input, yes, the two ROMs should be connected identically.

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