Re: strange read with a 6502...

perhaps crosstalk between bit 0 of the address bus and some data line? did you 
gate the address with the clock?

On Wednesday 30 March 2016, 11:20:26 didier derny <didier@aida.org> wrote:
> not really specifically tested at other addresses but initially I found
> that my code was working or not working
> simply by editing the code, it was a long process to reduce the code to
> 2 instructions
> 
> I can try at several addresses
> 
> in anycase the chip is always at the same address. it's decoded by a
> 74LS138 + 74LS04
> 
> as the ch376 is faster than the 6502 I was thinking that the data could
> be removed from the bus
> by the ch376 before the 6502 got them...
> 
> but why do I find a difference when the code doing the read is placed at
> odd or even addresses...
> 
> the ch376 as 2 ports    DATA  and COMMAND/STATUS
> 
> this code read the directory of usb key
> if the read is at odd addreses I get the right directory content
> if the read is at even addresses I get 00
> 
> the commands works, reading the directory involves several commands all
> working
> 
> On 30/03/2016 10:37, A. Fachat wrote:
> > Am 30. März 2016 10:15:24 schrieb didier derny <didier@aida.org>:
> >> I have a problem with a read with a 6502
> >> 
> >> I read a data on a register (from a CH376S)
> >> 
> >> I have the following code:
> >>                      *= 2000
> >> 
> >> readdata      LDA    CH376data
> >> 
> >>                       RTS
> >> 
> >> this code always get  the wrong value
> >> 
> >>                      *= 2001
> >> 
> >> readdata     LDA    CH376data
> >> 
> >>                       RTS
> >> 
> >> now with this code I get the right value...
> > 
> > That could be a broken address line to the IO chip or a timing issue
> > in the address decode depending on the addresses.
> > 
> > André
> > 
> >       Message was sent through the cbm-hackers mailing list
> 
>        Message was sent through the cbm-hackers mailing list

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