Bankswitching in UNROM

[Dracula X]

So I finally know how to bankswitch in UNROM but the tricky part is where to put the code in a new location. It could be reprogram the whole code or some. How I found out where to put the new code is to use the code/data/logger to find out where to put the code at that's highlited in "Dark-yellow - the byte is code" in Hex Viewer while the code is finished logging.

[KingMike]

So you know about the "bus conflicts" thing?
Where you must always write the ROM bank to a ROM address with the same value you want to write?

[Dracula X]

Not yet but I'll give it a try!

I'm using this methood: http://wiki.nesdev.com/w/index.php/Programming_UNROM
I had the ROM expanded to 256kb.

[KingMike]

Yeah, typically games would do something like putting a list of bank numbers (00, 01, 02, etc.) at, say $C000.

Then a bankswap function would be like
(say A was the desired bank number)
TAY
LDA $C000,Y
STA $C000,Y

[Dracula X]

OK! Now I understand how this works! I use Bus Conflict this time and now I know where to put the new code.

Example:

Code Select Expand


$9000 ; Bank 03
Test:
        lda #$07
        jsr bankswitch
------------------------------------------------------
$9005 ; Bank 07
newcode:
        ldy #51
        newcode2,y
------------------------------------------------------
.org $8000 ; Bank 07
newcode2:
        .byte $03,$03
------------------------------------------------------
That's it!

The code is from "The Guardian Legend".