mk79 wrote:Do all capacitors on your board look like a resistor?
I see you answered this yourself.
![Laughing :lol:](./images/smilies/icon_lol.gif)
I don't remember seeing capacitors with resistor type markings that are very confusing they are normally like the yellow ones between the RAM chips.
I have fixed my home made ROM board I think because everything has gone more stable and it looks like it is just the RAM now. The screen and background always come up the same with the same background.
mk79 wrote:- The first value you see on screen is the 32-bit value written, the second the one read back. So your D0 bit is stuck high.- If bit 0 was low in the displayed picture this would point to IC21. Your picture is pretty bad quality to tell much, but it looks like bit 0 is stuck high in the displayed picture, too (the white stripes). Meaning that either IC1 and IC9 are both faulty or, more likely, that one of the chips or something else pulls the line high. Basically it boils down to IC1, IC9, IC21 and IC22. Or some other bridge bringing D0 high on the ULA bus side.
Yes I thought bit 0 was the problem but after looking at the numbers I have seen it change state so it isn't stuck. What appears to be happening is it depends on what value was previously set. I am not 100% sure but it looks like if it does get changed it is held so I had a look at the selection signals on the buffer. The R/W pin 1 is working but I am not sure about the !OE from the HAL chip. It has a regular 25 nS pulse down. Other pins on the HAL have loaded rise times like a capacitor charge up curve that takes over half their pulse width to get over 80% that I would not be happy with if I had designed it. Any suggestions on verifying the HAL chip or what to next would be appreciated.