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Old 12th Sep 2017, 9:49 pm   #11
PETERg0rsq
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Join Date: Jun 2009
Location: St Helens, Lancashire, UK.
Posts: 641
Default Re: Help with 6802 Microcontroller

Wow...what a great response

Some good suggestions, which I will certainly follow up.

I will try and answer as many questions/comments as possible.

I have read all the ROM and EPROM chips. I read them several times and got validation between each read, so I believe my eprom programmer is reading them OK. I can certainly upload a copy, but I would not want to put anyone through too much trouble...just yet.

I do not believe there is a problem with the ROM/EPROMs as the signal generator will boot and run, maybe 1 in 100 starts! I could re-burn the EPROMS, but not the ROM. Certainly worth a try.

The signal generator is an Adret 742A 2.4GHZ RF generator (never seen one before, but has CPU board and front panel same as Adret 730A.). It is my main generator. I bought it about 2 years ago not working, and fixed a fault in one of the DAC's, and used it regularly until about 2 weeks ago when it just failed to fully power on. I powered on and off a few times and it worked for a short while, then failed again, and is where I am today!

I have tested the operation of the reset circuit, and it works fine. PA monitors the floating 5V line, and when 5V it is up, PA turns ON and applies 5V to RESET.
When the 6802 sends out an 1000 to 17FF hex address the RESET line is driven low via SN1, SN6 and SN3. I will replace both capacitors though as a precaution.

My diagnostics have not lead me to C25, as do not really understand the function, other than pulses the PIA CB1 interrupt flag. I do not know the meaning or function of "MONO" (french abbreviation!) Unfortunately I can not read the PIA as it is hidden behind a heatsink!
Again worth replacing the capacitor.

I like the possibility of there being a watchdog timer, but how to see it?

Tonight I will get a full reading of the 6801 ports during a failed boot, and see what I can read.

The information from MrBungle yesterday was very helpful in understanding how the 6802 boots from the ROM. I had read the data sheet many times before, but not understood the booting references.
I can see the top two Bytes on my logic diagrams from the logic analyser as the first instructions as it boots.

Sometimes the 6802 will stop due to an external reset, and sometimes it seems to just keep on running (when successfully boots it boots up, then WAITs for an interrupt from the front panel (INT.CLAV/MAN) then wakes up and processes the information, then WAIT for next interrupt.
However the boot to fail time is variable.

David, all the address and data bits change during the booting (I will post a picture of the activity later), but I noted that before the RESET goes high to start the booting, that all the Address pins are LOW, except A0 which is HIGH!

I think that covers it.

Tonight I will try and capture a good boot sequence, as well as a bad boot sequence (reading the ports on the 6802) and see what differences I can observe. I should also be able to read what the program is doing by observation.

First to replace those capacitors (without dislodging all my probes)

Thanks again
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