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Commodore PET 2001 with no cursor

Harald,

Can you confirm exactly what the configuration of your machine is now please.

Is this using emulated RAM and ROM on the ROMulator (bypassing PETs RAM and ROM)?

Do you have all of the PIAs and VIA installed or not?

Dave
 
Hi all,
What I've noticed since is that the cassette motor runs all the time, I remember it should stop about 2 seconds after booting. maybe another clue to the error.
Harald
 
I suspect the faults may be linked. But equally probable is that they are not.

Anyhow, I would proceed as follows:

1. Remove PIA B8. This is only used for the IEEE488 port. Removing it would remove a source of confusion.

2. Boot the PET until you get the READY prompt but no cursor.

3. Check CPU pin 7 (SYNC) for signs of activity/pulses. This indicates that the CPU is still executing instructions. If the CPU has ‘crashed’ it is not executing instructions, and the cursor can’t flash...

4. Check CPU pin 4 (/IRQ) for signs of activity/pulses. If this pin is permanently HIGH then we need to find out why.

My ‘bet’ is a faulty PIA (or two)...

Dave
 
No interrupt then - hence no blinking cursor...

Can we just go back to pin 18 of PIA G8 please and check for pulses there.

If not, can you replace the PIA at G8 for the other PIA that you have and repeat the measurements please.

EDIT - you beat me to the PIA swapping!

Dave
 
So, you either have two faulty PIAs (has been known) or a faulty VIA.

This was why I was hoping to get my PETTESTER working to test out the keyboard PIA...

Which version of BASIC are you using on the ROMulator out of interest?

Dave
 
What do you mean by “works”?

Does the cursor flash and is the keyboard work with these settings?

Dave
 
No problem.

So, you can either order some replacement PIA and VIA devices and hope that fixes the problem, or we go back and try to get my PETTESTER firmware working to test the existing keyboard PIA. Or we could do both...

Your choice...

Dave
 
I have 1 PIA and 1 VIA as spares but I get the same result with all of them. The high level at CPU pin 4 is also without all PIAs and VIA and even without CPU. Where else can it come from? I can't see any other source on the schematic.
Harald
 
Correct. The /IRQ line only comes from the two PIAs and the VIA.

This is an open collector signal, and there is an external pull-up resistor to +5V (hence it is high without any of the chips in).

Good that you had some spares...

What I am thinking now is that the PIA and/or VIA are not being selected properly (an address problem) or the correct data is not being written to them to initialise them correctly.

I’ll need to think about that one for a while to see what tests I can come up with...

Good investigative work though.

We’ll solve it!

Dave
 
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