trying to make mapper 140 bank switching question.

A place that you can discuss reproduction of classic titles or "licensed-for-reproduction" homebrew for personal use.

Moderators: B00daW, Moderators

Forum rules
1. NO BLATANT PIRACY. This includes reproducing homebrew less than 10 years old, with the exception of free software.
2. No advertising your reproductions, with the exception of free software.
3. Be nice. See RFC 1855 if you aren't sure what this means.
Post Reply
nes gamer
Posts: 9
Joined: Wed Apr 15, 2015 9:03 pm

trying to make mapper 140 bank switching question.

Post by nes gamer »

hello everyone I am sorry if this sounds like a stupid question but can somebody please explain this to me. I am trying to make a mapper 140 out of an GNROM cart. It is to make Bashi Bazook. Thi is a line from amother page and I am not exactly sure how to do this...
Placing the bank register in $6000-$7FFF instead of $8000-$FFFF gives mapper 140.
can some please explain this as I am not to savy on bank switching but would love to learn thank you all in advance.
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: trying to make mapper 140 bank switching question.

Post by lidnariq »

You'll need to replace the 74'161's clock input with NAND4(CPU A14, CPU A13, /ROMSEL, M2).
nes gamer
Posts: 9
Joined: Wed Apr 15, 2015 9:03 pm

Re: trying to make mapper 140 bank switching question.

Post by nes gamer »

I am sorry is this a rewiring change or a programming change. Again I am sorry if these are stupid questions just can't seem to find a lot of info for explanations of these things. And I am not sure if it is a rewiring thing which pins need to go where.
tepples
Posts: 22708
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
Contact:

Re: trying to make mapper 140 bank switching question.

Post by tepples »

Essentially you'll be wiring the PRG RAM decoding circuit of Family BASIC onto your cart board. Except instead of running the output of the 7420 to a RAM's enable, you run it to one of the control lines of the 74HC161 or 74HC377 that holds the bank number.
nes gamer
Posts: 9
Joined: Wed Apr 15, 2015 9:03 pm

Re: trying to make mapper 140 bank switching question.

Post by nes gamer »

OK thank you for the explaintion. unfortunately it seems like it is over my head. I am good with rewiring through schematics but I really get confused with the bank switching stuff. Does anyone happen to have info on what rewiring specifically needs to be done for Bashi Bazook. Again thanks to all.
Post Reply