exxos's Atari, Amiga & retro forum

Could you put the Kickstart ROM in please. We know that the ROM is OK and has the right pin-out. It was also showing more life for longer when you had it in there.

OK. I just nipped to my parents house but once I return home, I will put the Kickstart ROM in. Thank you Stephen for your help, and more importantly, your patience!

I inserted the Kickstart ROM, reset the motherboard and this is a sample of the output. It continues for about 15 seconds: This is an image of the output for both with the trigger set to 392mV:

I think I have done it - but not with the parameters you specified.
Yellow is AS and blue is ROMEN.
This is with the Diagrom after a reset:

Well, given that it's running code for 15 seconds before halting with the Kickstart ROMs as opposed to a few instructions with the DiagROM ROM it looks like it can probably read the ROM OK.

I would suggest that the DiagROM chip is either the incorrect pinout for your motherboard or it is faulty.

We can now move on and try to see if we can find out what's happening.

Do you have any display output at all when you power up? The early part of the Kickstart boot initialises the display. From what I understand it tries to use the background colour as a sort of diagnostic, e.g. yellow for some sort of failure etc.

If it's not initialising the display it suggests that either that art of the hardware is faulty or it can't talk to it because something it needs to go through isn't working.

I know the Diagrom is fine as it works in another board.
I know what you mean by the different colours on start up but unfortunately only black is displayed, not even a dark grey.

Right im happy ROMOE is working. I'm back to data/address bus issues.

Is there a way to test the two 74LS245 bus buffers to determine if they are working correctly, other than removing them from the board?

Kepler wrote: 16 Jun 2024 21:43 Is there a way to test the two 74LS245 bus buffers to determine if they are working correctly, other than removing them from the board?

If you look at the datasheet for the 245 you'll be able to see which pins tally for each bus, e.g. Pin 2 and Pin 18 are one pair. You can check each side to see if the two sets of data look similar. You can also check Pin 1 to see if that's going up and down as that specifies which direction the data is flowing through the chip. (If it's not going up and down then there's likely a problem with what's driving that signal.)

Each 245 is communicating 8 bits, so that's half the bus.

Anyway, first things first, 'scope each of the pins to see if one has less data flowing than all the rest would be my next plan (and checking that Pin 1 is toggling).

scope each of the pins to see if one has less data flowing than all the rest - do you mean on the CPU or the bus buffers?