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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
ADC bug, CPU fried ?
Hi,
I have this code:
_index .byt 2
LDX #0
CLC
.re LDA _number
ADC #8
STA _number
INX
CPX _index
BNE .re
This should give 24 or not ?
Nomatter where I place the CLC,
it always gives +2
2 times 8 gives me 18
Is my 6510 fried ?
Jan |
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Hoogo
Registered: Jun 2002
Posts: 105 |
_number is not initialized. You add 16 to an unknown value. |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
ah, this example has no init, but the real code does. :-) |
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hollowman
Registered: Dec 2001
Posts: 475 |
you have a c64 which can load or assemble code and run
it, but it cant add correctly? interesting.. |
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JackAsser
Registered: Jun 2002
Posts: 2038 |
The example above should add 16, not 24. But 18 seems weird.... Are you telling us the whole truth here? Is it really initialized, do you have IRQ that destroy A and X etc... And since CPX _index sets C=0 when X<_index it's ok to have the CLC before .re.
And Hollowman has a REALLY good point. |
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SIDWAVE
Account closed
Registered: Apr 2002
Posts: 2238 |
i dont know whats wrong, its so weird.
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WVL
Registered: Mar 2002
Posts: 924 |
bring your machine to x and show us ;) |
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WVL
Registered: Mar 2002
Posts: 924 |
too bad i didn't get to see your machine and see it for myself.
anyway, i can't believe this bug is actually happening.. |
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Perff
Administrator
Posts: 1686 |
@Rambones
Perhaps if you somehow post the machinecode generated by the assembler, we could find an answer? Perhaps the assembler does something strange?
There shouldn't be that many hex-numbers to post for that small code. :)
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JackAsser
Registered: Jun 2002
Posts: 2038 |
Ofcourse it wasn't any HW bug as we all said... :D Rambones and some other dude found out the _SW_ at X and he came to me dead drunk explaining the bug. It was something that wrote garbage in the memory somehow. Anyway.... I could barly hear him since he was absolutly dead drunk. You really have too look for more drunk persons... :D |
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WVL
Registered: Mar 2002
Posts: 924 |
Good ;) that's another 'mystery' solved ;)
it was ofcourse impossible the cpu had problems adding. The whole c64 would never have been able to boot to the basic editor..
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