Quote:
Originally Posted by retromit
One thing I did notice when the PET booted was that there was no flashing cursor. I did try and swap the 6520s around in UC6 and UC7, but on doing this (after powering on the PET) I weas greeted by a blank screen. On swapping the 6520s back again, I had the boot screen and no cursor.
The next test was to run the Slothie EPROM in UD9. On powering up the PET it started to run, but gave the following error (picture also attached):
KB : E0 !
So I guess this is down to the potential issue with the 6520?
Tim.
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Well done for checking the processor, lucky you had a spare as that could have been hard to diagnose. If you buy one to replace it be careful as there are a number of variants - the modern WDC 65C02 is not quite pin compatible (if I recall you need to disconnect a pin or something).
I would expect to see the 10 hex scan codes across the bottom, not just one. Also I note the '0' in the top right hand corner is still 0, this should be counting up 0-9 then going round again, at approximately 1 sec intervals. This suggests to me that there is a problem with the interrupts, this could be caused by a faulty I/O chip (6520 or 6522). The interrupt source is the vertical retrace from the video circuitry. It looks like the keyoard scan is getting interrupted, this could be caused by continual interrupts causing the stack to overflow?
Its also possible it is a RAM refresh problem, although BASIC seems to start OK.
If you press a key it is supposed to show which key was pressed. the "!" key would normally show the first scan code as "FE" and all the others as "FF".
A screenshot of the diagnostic with no keys pressed is attached.