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Forums > C64 Coding > address for changing pointers for rts?
2006-02-11 01:23
midiland
Account closed

Registered: Nov 2004
Posts: 4
address for changing pointers for rts?

Hey guys

I need a reminder of the addresses used for when I need to change an address for a "rts" so it returns to a new location rather than the old

eg

jsr blah
rts
blah rts

but instead of returning to the jsr'd address to go to a new address

Thanks!!

I cant remember the mem locations to change it :(
2006-02-11 02:05
Style

Registered: Jun 2004
Posts: 498
PLA
PLA
LDA #<new address
PHA
LDA #>new address
PHA

or similar :) During a JSR the return address (PC + 2) is pushed to the stack. I think its in low byte/high byte order.

Obviously during an RTS the address is then pulled from the stack.
2006-02-11 02:13
midiland
Account closed

Registered: Nov 2004
Posts: 4
Ahhh thats it...!!!!

Thanks mate!

2006-02-11 12:36
Graham
Account closed

Registered: Dec 2002
Posts: 990
Not quite, you must store "address-1" to stack if you want to return to the opcode after the JSR.
2006-02-11 12:39
Ninja

Registered: Jan 2002
Posts: 419
PLA
PLA
JMP new_adress

is shorter and faster. And as we are at it:

JSR somewhere
RTS

can be replaced with

JMP somewhere

which is also shorter and faster.
2006-02-11 14:33
Style

Registered: Jun 2004
Posts: 498
He'll figure it out :)
2006-02-11 15:34
Oswald

Registered: Apr 2002
Posts: 5129
ninja, indeed, this question smells me some horrible coding style
2006-02-11 15:55
JackAsser

Registered: Jun 2002
Posts: 2038
@Oswald: That coding style have saved me quite some times. =) But yes, horrible indeed.
2006-02-11 16:45
Zyron

Registered: Jan 2002
Posts: 2381
You naughty boy :)
2006-02-12 09:41
Monte Carlos

Registered: Jun 2004
Posts: 370
If Steve Wozniak used it in its Sweet 16 asm style interpreter
for the Apple II, why should we not use it?
2006-02-12 16:44
Cruzer

Registered: Dec 2001
Posts: 1051
I prefer

        jmp subroutine
back:

subroutine:
        jmp back


for subroutines that are only called from one place, e.g. typically speedcode, since it saves 6 cycles. No coding style is horrible if it saves cycles :)
 
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