exxos's Atari, Amiga & retro forum

i have the multi diagnostic card, not entirely sure how the serial bit works, does it just show on a comms terminal on pc side ?

alienkidmj12 wrote: 09 Sep 2021 10:16 i have the multi diagnostic card, not entirely sure how the serial bit works, does it just show on a comms terminal on pc side ?

So set up a terminal on your PC with 9600 baud 8 N 1 and then connect the ST to it via a null modem cable and USB adaptor etc.

If your ST is sort of working, the text you would see outputted to the screen would also be outputted via serial. If there is a fault with ram for instance, then you'll get a repeated error code listing the ram fault.

This presumes that the CPU isn't halted, so just to verify that I'd put. your multimeter on pin 17 of one of the expansion sockets and the other on ground. Press reset and if the CPU is working, you'll have a permanent 5v. output on that pin that dips to 0v when the reset button is pressed.

ok so which would be pin 17, goes upto 0.14v when i hold reset

cheers

This is a handy pic I use that shows all pins on the 68K socket

i'm only getting 0.10v from pin 17,goes upto 0.14v when i hold reset

cheers

alienkidmj12 wrote: 09 Sep 2021 10:50 i'm only getting 0.10v from pin 17,goes upto 0.14v when i hold reset

cheers

What happens when you do the same with pin 18?

getting 3.85v from pin 18,goes upto 0.15v when i hold reset

Ok, I'm presuming you are using a 5v socket for the diagnostic right? If not then please do the same on say socket 1 or 2.

You should have around 5v on pin 18 without the reset pressed. When you press reset it'll go low as you're seeing.

With pin 17, the /Halt pin, this goes low when you press the reset but then should go high 5v when you release the reset. It may be that it is doing this very quickly but then something else is telling the CPU to halt or not to run.

Remove the DMA chip and try the reset button thing on 17 again please.

pin17 0.10 reset 0.14

pin18 5.14 reset 0.15