• Please review our updated Terms and Rules here

Cbm 2001 Pet strange boot

They look fine.

I am not sure why your frequency meter is not stable. The oscilloscope trace is rock solid though. You may need to read the manual to identify how the internal frequency meter works and whether there is any specific set-up required for it (e.g. oscilloscope Y position or triggering requirements).

I will post some more points for you to check tomorrow - but (to start you off) there is a small piece of logic in the upper left-hand corner of schematic number 1 providing the direction signals for the octal databus buffers. Where you see a buffered address line identified (BAn) can you check the pin of the associated IC to make sure that the frequency is as expected.

Dave
 
They look fine.

I am not sure why your frequency meter is not stable. The oscilloscope trace is rock solid though. You may need to read the manual to identify how the internal frequency meter works and whether there is any specific set-up required for it (e.g. oscilloscope Y position or triggering requirements).

I will post some more points for you to check tomorrow - but (to start you off) there is a small piece of logic in the upper left-hand corner of schematic number 1 providing the direction signals for the octal databus buffers. Where you see a buffered address line identified (BAn) can you check the pin of the associated IC to make sure that the frequency is as expected.

Dave

A4 PIN2
B2 PIN 1,2,4
A3 PIN3

Correct?
 

Attachments

  • Schermata 2022-06-24 alle 20.56.44.png
    Schermata 2022-06-24 alle 20.56.44.png
    35.6 KB · Views: 10
Yes,

You can also check A3/4 and B2/5 at the same time. These are an inverted BA11 and can be tested at the same time.

Thanks for posting the image, that helps me help you!

Dave
 
A4 PIN2 waveform and 0.00762 KHz
B2 1 waveform and 0.976 KHz
B2 2 waveform and 0.488 KHz
B2 4 waveform and 0.244 KHz
B2 5 waveform and 0.122 KHz
A3 PIN3 waveform and freq changes from 0.122 and 0.130 Khz
A3 PIN4 waveform and 0.122 Khz
 
Can you video the following signals please and indicate the frequency (if the signals are stable).

B2/6.
A3/11.
A4/1.
A3/10.
A4/3.
A4/6.

Dave
 
A4 PIN2 waveform and 0.00762 KHz
B2 1 waveform and 0.976 KHz
B2 2 waveform and 0.488 KHz
B2 4 waveform and 0.244 KHz
B2 5 waveform and 0.122 KHz
A3 PIN3 waveform and freq changes from 0.122 and 0.130 Khz
A3 PIN4 waveform and 0.122 Khz
Desperado, you are getting good with the scope. Practice makes perfect. Be careful and do not touch/short adjacent pins.
 
Good point, I was going to mention that a while ago and forgot.

The probes cone with plastic attachments. They cover the GND ring of the probe to protect it from shorting against things. In addition, one of the plastic attachments helps the probe to stay on IC pins and not slip.

Are you using these plastic attachments?

Dave
 
Good point, I was going to mention that a while ago and forgot.

The probes cone with plastic attachments. They cover the GND ring of the probe to protect it from shorting against things. In addition, one of the plastic attachments helps the probe to stay on IC pins and not slip.

Are you using these plastic attachments?

Dave
I am currently using the probe normally but there is a small package with these accessories inside
 

Attachments

  • Schermata 2022-06-25 alle 10.28.09.png
    Schermata 2022-06-25 alle 10.28.09.png
    902.2 KB · Views: 6
The probe tip I was referring to is the yellow one in the lower of your photograph.

If you use the probe without a plastic tip, you can accidentally short something out.

Equally, the point tip can slip off IC pins. The plastic tip can help prevent this.

The black screwdriver is for adjusting the probe when using the squarewave test signal. Failure to adjust the probe correctly can result in strange reading phenomenon. Read the manual that came with the probe as to how to adjust it.

Dave
 
As I understand it, at the moment we are trying to work out why the CPU won't implement the code in the Daver2 program, burnt unto UD9 to write to the first screen element (character position) at address $8000 . Are you still running Daver2's program in UD9 ? or did you go back to the NOP generator to check the frequencies on the address lines ?

So given that you have not found any obvious problems where you have tested so far, you might want to consider what I posted in #1603 (I would suggest doing this with the Daver2 UD9 ROM running in UD9 because as that program loop runs there are Reads & Writes happening on the data bus )

"I think the R/W control line from the CPU pin 34 via A10 pin 3&4 and A5 pin 4 & 6 to E9 &E10 (data read & write buffers) needs to be scoped. Also A4 pin 9 & 8".

Sometimes it can be a hunt to find the faulty part/s.
 
Last edited:
With the NOP generator to start with.

Remember, with the NOP generator, the CPU is only fetching and executing NOP instructions, so the R/W (and hence BR/W) signals should always be HIGH. This is still a useful test though...

We haven't finished the previous tests yet though. Some of the signal videos are unusable, as the oscilloscope trace is not synchronised to anything - so I can't see what I need to. This will involve some more learning in how to use the external trigger of the oscilloscope though.

Dave
 
With the NOP generator to start with.

Remember, with the NOP generator, the CPU is only fetching and executing NOP instructions, so the R/W (and hence BR/W) signals should always be HIGH. This is still a useful test though...

We haven't finished the previous tests yet though. Some of the signal videos are unusable, as the oscilloscope trace is not synchronised to anything - so I can't see what I need to. This will involve some more learning in how to use the external trigger of the oscilloscope though.

Dave
Hi Dave, what sign doesn't convince you?
 
Back
Top