Converting MHROM CHR 32k to 64k?

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lidnariq
Posts: 8792
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Converting MHROM CHR 32k to 64k?

Post by lidnariq » Fri Feb 20, 2015 10:03 pm

You've got to be miscounting pins.

guitarzombie
Posts: 164
Joined: Sat Dec 07, 2013 6:18 pm

Re: Converting MHROM CHR 32k to 64k?

Post by guitarzombie » Fri Feb 20, 2015 10:38 pm

Im def not.

Anyway I tried another one with a CNROM 256-161 board, same diagram and got glitchy graphics again, even tho the mirroring is right too... hrm.

guitarzombie
Posts: 164
Joined: Sat Dec 07, 2013 6:18 pm

Re: Converting MHROM CHR 32k to 64k?

Post by guitarzombie » Fri Feb 20, 2015 11:14 pm

I tried switching the mirroring, and using D3, D4 and D5 and it was worse. So its def D2 and the graphics are all a mess. Im thinking the chip I got was over erased. Gonna chuck it and try again. I hate when i waste all that time for nothing.

And I gotta figure out how my Super Mario Unlimited is working but with NO sound at all (?!) AND i gotta figure out the MHROM 161 altho i have a feelling it just might not work at all, or i have to disconnect some stuff... at least i got a better understanding now.

guitarzombie
Posts: 164
Joined: Sat Dec 07, 2013 6:18 pm

Re: Converting MHROM CHR 32k to 64k?

Post by guitarzombie » Sat Feb 21, 2015 8:06 am

Ok I got it. For the CNROM-161 board, I was right the CHR chip was bad straight from the package. Swapped it, and worked. Now for the MHROM board I couldn't figure out why so I checked the pinout of the 161 I did. I saw that it controls PRGs A15 even tho i wasn't using it. I lifted pin 1 of the prg and poof worked (after I set the mirroring)

Interesting that these games when the mirroring is wrong you get a LOT of glitchy graphics not like, lets say SMB where the game works with fine the graphics but 'loads' them to the screen wrong. So all this time I was thinking those bad graphics were from a bad chip or soldering or whatever.

Anyway I learned something and isn't that the most important? :) Thanks for the help.

LORD_Crusher
Posts: 1
Joined: Fri Jun 03, 2016 8:13 am

Re: Converting MHROM CHR 32k to 64k?

Post by LORD_Crusher » Fri Jun 03, 2016 8:21 am

guitarzombie wrote:Then how is it this wiring diargram

PRG:
Pin 14 (GND) to 161 pin 12
CHR:
Pin 1 (A15) to 161 pin 5.

Works for CNROM-07s to make the CHR 64k when you're grounding the output pin of the 161 and a15 goes to the input? I know this cuz its worked for me.


EDIT! SUCCESS! (Kinda)

I took what you said and looked up the 161 and it made sense, so I did a check on the wiring diagram for the CNROM 256-161 and it seemed like D0 went to A13 and D1 when to A14, so using the 161 I connected D2 to A15 and boom! (I just had to set the mirroring). Great! Now ill get a better understanding of the MHROM.
I know the last post was over a year ago, but can you upload a wiring diagram of your work? I'm trying to build a Panesian game and i only got grafic garbage.

Ice Man
Posts: 368
Joined: Fri Jul 04, 2014 2:34 pm

Re: Converting MHROM CHR 32k to 64k?

Post by Ice Man » Fri Jun 03, 2016 12:45 pm

Panesian -> CNROM Conversion (mapper 3):
Bend up pin 5 and 12 of 74HC161
Connect pin 5 to D2 of PRG ROM
Connect pin 12 to A15 of CHR ROM

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