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Forums > C64 Coding > Tape loader working on c64, not on c128, why?

2018-12-08 17:44

tlr

Registered: Sep 2003
Posts: 1790

Tape loader working on c64, not on c128, why?

When working on a tape loader recently I was made aware by testers that it doesn't work on the C128 at all but reliably on the C64.

I haven't mananged to figure out what makes it so. Does anyone here have experience with this sort of problem.

I've considered $d030 and avoided any I/O mirrors. I'm kind of suspecting $00/$01 but can't really see why it would be a problem. (it's $2f/$06 during loading)

From the reports the problem is there already in make s-load 0.3. In emulation no problems show up on x64 vs x128. Haven't tried z64k yet.

2018-12-09 13:04

oziphantom

Registered: Oct 2014
Posts: 490

does it fail on 128 mode, or 64 mode?

my guess is the port on the 128 has an extra bit, which will still be there in 64 mode, so your code might assume that it is one way or the other, to which the 128 by default is the other.
Bit 6 which will be an input thanks to both the 128 kernal and the c64 kernal (i.e 0) is the Caps Lock Key which is most probably up in most cases and hence will read as a 0 not a 1 as it does by default on the C64. I guess try pressing in the CAPS/LOCK key ( not sure if that is "locked out" in 64 mode or not ) and see if that fixes the loading.

2018-12-09 13:29

tlr

Registered: Sep 2003
Posts: 1790

Thanks for the tip. I do not read $01 so it shouldn't be a problem but will make the testers try Caps Lock anyway.

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