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PostPosted: Wed Nov 16, 2016 6:50 am 
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I'm a newbie of making nes/fc reproduction cartridges. According to the nesdev wiki, I made a few mappers of the carts, like cnrom, mmc1, mmc3, vrc1... and many thanks those who provide so much detail information.

I used some cheaper flash chip and eeprom: en29f040, mx29f040 and W27C020. They are cheaper than AMD chips and work fine on the above mapper carts.

When I making namcot 163 and vrc4 carts, the problems came. both are blank screen when I replace the flash chip. the cheaper chips seems unfit the namcot 163 board well. So I designed a tsop2dip board to carry a tsop amd chip, like am29f080b (tsop nor flash chip is still cheaper than dip). am29f080b works better, #oe binded to #ce, the game can be played but the graphic is not right. I tried to bind #oe to GND, graphic is worst but the game still can be played. I also put 74hc00 in the circut to deal with the chr chip ce, but the graphic still not correct.

for vrc4 board, even using am29f080b burned with the original game to test, the screen is still blank... I put the original mask roms back and the cart run correctly. It means the board is ok.

Must I use a am29f040b to finish the reproduction? or what did I lost something?


Last edited by agentx on Wed Nov 16, 2016 5:28 pm, edited 1 time in total.

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PostPosted: Wed Nov 16, 2016 9:04 am 
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agentx wrote:
en29f040, mx29f040 and W27C020.
[...]
am29f080b [...] am29f040b
The AM29F080B holds 8 mebibits of data (1 MiB). The N163 and VRC4 can only address 512KiB. How are you preparing your data and/or rewiring your ROM to handle this difference?


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PostPosted: Wed Nov 16, 2016 5:35 pm 
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lidnariq wrote:
agentx wrote:
en29f040, mx29f040 and W27C020.
[...]
am29f080b [...] am29f040b
The AM29F080B holds 8 mebibits of data (1 MiB). The N163 and VRC4 can only address 512KiB. How are you preparing your data and/or rewiring your ROM to handle this difference?


I used 128k+128k game to test. a17~19 to GND, or to VCC with each 128k x8 as a whole 1024k bin file to be burned. Both had been tried.


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PostPosted: Thu Nov 17, 2016 2:30 am 
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agentx wrote:
I used 128k+128k game to test. a17~19 to GND, or to VCC with each 128k x8 as a whole 1024k bin file to be burned. Both had been tried.
Hm, well, that's correct.

agentx wrote:
I tried to bind #oe to GND, graphic is worst but the game still can be played.
You mean the PRG's /OE input?

Quote:
I also put 74hc00 in the circut to deal with the chr chip ce, but the graphic still not correct.
The NES/FC PPU's data bus is multiplexed, containing both address and data. If the ROM doesn't only respond when BOTH PPU/RD and PPU A13 are low it'll stomp all over something it shouldn't, producing incorrect graphics.

Did you mean 74'32? The 74'00 is a NAND gate, but which is the wrong function:
Code:
PPU/RD PPUA13 ROM/OE 74'00result
   0      0      0      1
   0      1      1      1
   1      0      1      1
   1      1      1      0


That said, you shouldn't need to. The ROM already has two active-low output enables, and (for the VRC4) connecting PPU/RD to ROM/OE and PPU A13 to ROM/CE is correct.

For the N163, you may need to change how you connect the CHR ROM(or RAM) depending on how N163 pin 33 is connected: viewtopic.php?t=14312 nesdevwiki:Namcot 163 family pinout


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PostPosted: Fri Nov 18, 2016 8:08 am 
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Quote:
That said, you shouldn't need to. The ROM already has two active-low output enables, and (for the VRC4) connecting PPU/RD to ROM/OE and PPU A13 to ROM/CE is correct.

For the N163, you may need to change how you connect the CHR ROM(or RAM) depending on how N163 pin 33 is connected: https://forums.nesdev.com/viewtopic.php?t=14312 nesdevwiki:Namcot 163 family pinout


Thanks for you advise! I will revise the circuit from your opinion. and one more question, in Vrc4, when ppu/rd to rom/oe and ppu a13 to rom/ce, should be Vrc4's pin10 (chr/ce) and pin12 (ppu/rd) left float, or still connected? if let them float, I shall cut the route on the board. :roll:


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PostPosted: Sat Nov 19, 2016 3:39 am 
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agentx wrote:
in Vrc4, when ppu/rd to rom/oe and ppu a13 to rom/ce, should be Vrc4's pin10 (chr/ce) and pin12 (ppu/rd) left float, or still connected? if let them float, I shall cut the route on the board.
Your choice, both should be acceptable. (There is no need to cut pin 12 regardless)

nesdevwiki:VRC4 pinout

Either: VRC4 CHR/CE to CHR /CE, ground to CHR /OE; or
PPU A13 to CHR /CE, PPU /RD to CHR /OE

The NES's commercial era came from a time when the 28-pin packages were so much cheaper than any larger package that basically everyone was using 28-pin 128 KiB mask ROMs, with only a single output enable. So the VRC2 and VRC4 include some support hardware to combine PPU A13 and PPU /RD into CHR /E


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