Re: Weird /KERNAL line on old boards

On 07/08/2018 02:37 AM, Nejat Dilek wrote:
> 
> Here are my findings,
> 
> 1. In similar scenario /BASIC line is clean.
> 
> 2. /KERNAL line is clean if KERNAL is switched off  using processor
> port. (Obviously this is not enough for my adapter to work)
> 
> 3. The duration of these sporadic chip selects are around 41.67 ns and
> aligns with PHI2 high. (I don't know if it's accurate since I measure
> this with a 24mhz logic analyzer)
> 
> 4. Turning off VIC display doesn't help.
> 
> 5. Signal is dependent on what is displayed on the screen. If screen
> is empty then it even goes to full 1mhz 0.5us low / 0.5 high with 41us
> intervals between these accesses.

You might want to also take a look at the Char-ROM output of the PLA, 
that one also shows interesting things.

Remember that the original PLA for the C64 was a Signetics 82S100. It is 
purely combinational with a delay in the range of 50ns , no registers 
involved. Commodore also used the Fairchild 93459, which is a clone of 
the 82S100 and the 906114-01 is a mask programmed clone of the 82S100.

  Gerrit