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Thread: Commodore pet 3032 screen full of lines

  1. Default

    Quote Originally Posted by daver2 View Post
    I can't see anything wrong with that. As Alice would say "curiouser and curiouser"...

    Next issue could be that your kernel ROM is (in some way) different to what I am expecting...

    Each of the different variants of the kernel ROM (and the EDIT ROM) had a different entry point. I have configured my diagnostics to be compatible with all of the known variants of the Kernel ROM I know about. This included 901465-03 for BASIC 2.

    My diagnostics were originally written for an 8032 with BASIC 4 and (if I remember correctly) a similar thing happened when people used the diagnostics with BASIC 1 and 2 (hence the reason I added the three different entry points into my diagnostic ROM).

    Can you dump the kernel ROM out you are running please (in HEX) and post it so I can see where it enters the EDIT ROM please. The other option is to get your EPROM programmer to perform a 16-bit checksum on the contents of the ROM. It should match with $7C98.

    Thanks.

    I suppose the other problem is that we could have an address, data or ROM selection fault which is causing the diagnostic ROM not to execute correctly?

    Dave

    Please how can i dump the kernal in hex?
    Must i download 901465-03.bin and convert in hex?
    Thanks!

  2. Default

    Daver2 i dumped my kernal with programmer and i inserted here.
    Thanks
    Attached Files Attached Files

  3. #63
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    Default

    Thanks.

    That is exactly what I am expecting...

    The reset vector points to $FCD1 and the instructions at $FCD1 end up calling a subroutine at $E1DE (which is the entry point into my diagnostics from the kernel for BASIC 2).

    Can you use your logic probe to check two pins of the 6502 CPU (UC4) please. These are pins 4 (/IRQ) and 6 (/NMI). Both of these pins should be permanently 'HIGH'. If not, a rouge interrupt or NMI is being generated. This will upset the diagnostics - as the Kernel will probably end up entering the diagnostic ROM at some location that is not programmed to accept an entry.

    Dave

  4. Default

    Quote Originally Posted by daver2 View Post
    Thanks.

    That is exactly what I am expecting...

    The reset vector points to $FCD1 and the instructions at $FCD1 end up calling a subroutine at $E1DE (which is the entry point into my diagnostics from the kernel for BASIC 2).

    Can you use your logic probe to check two pins of the 6502 CPU (UC4) please. These are pins 4 (/IRQ) and 6 (/NMI). Both of these pins should be permanently 'HIGH'. If not, a rouge interrupt or NMI is being generated. This will upset the diagnostics - as the Kernel will probably end up entering the diagnostic ROM at some location that is not programmed to accept an entry.

    Dave

    pin 4 and 6 on Cpu are High!

  5. #65
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    Default

    That is good.

    All I can now think of is that there is a data, address or selection problem on the PET logic itself that is interfering with the correct operation of the diagnostic ROM. This will also interfere with the correct operation of BASIC - which is what you are also seeing.

    Let me have a think, and it will give dave_m a chance to catch up with what we have been up to.

    Would you be willing to consider the purchase of a cheap and cheerful oscilloscope to help you out with fixing these PETs (and any other machines in the future)? I have bought a little LCD single channel unit from a China via e-bay and it only cost me 20 or so pounds.

    Dave

  6. Default

    Quote Originally Posted by daver2 View Post
    That is good.

    All I can now think of is that there is a data, address or selection problem on the PET logic itself that is interfering with the correct operation of the diagnostic ROM. This will also interfere with the correct operation of BASIC - which is what you are also seeing.

    Let me have a think, and it will give dave_m a chance to catch up with what we have been up to.

    Would you be willing to consider the purchase of a cheap and cheerful oscilloscope to help you out with fixing these PETs (and any other machines in the future)? I have bought a little LCD single channel unit from a China via e-bay and it only cost me 20 or so pounds.

    Dave

    Ok if necessary i'll buy one scope. With logic probe it's not possible check ic logic?

  7. #67
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    Default

    The problem with a logic probe is that it tells you when something is high, low or pulsing. Sometimes you may get a little more information - but that is the basics.

    What I think you need to do next is to construct a NOP generator for the CPU to sit in. This will allow you to look at the address lines of the processor at different parts of the circuit. A0 should oscillate at twice the frequency of A1. A1 should oscillate at twice the frequency of A2 and so forth. At the same time as looking at the frequency, we need to check that there is a 'healthy' square wave present rather than some horrible looking waveform that may indicate two things (e.g. logic networks) are accidentally shorting together somewhere. Realistically, you can only do this with an oscilloscope.

    Dave

  8. Default

    Quote Originally Posted by daver2 View Post
    The problem with a logic probe is that it tells you when something is high, low or pulsing. Sometimes you may get a little more information - but that is the basics.

    What I think you need to do next is to construct a NOP generator for the CPU to sit in. This will allow you to look at the address lines of the processor at different parts of the circuit. A0 should oscillate at twice the frequency of A1. A1 should oscillate at twice the frequency of A2 and so forth. At the same time as looking at the frequency, we need to check that there is a 'healthy' square wave present rather than some horrible looking waveform that may indicate two things (e.g. logic networks) are accidentally shorting together somewhere. Realistically, you can only do this with an oscilloscope.

    Dave
    Sir Daver2
    is there nothing more I can do now with the probe ??? (

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