I just found out, one leg is brocken/missing on my GnR.
CN21, leg pin nr: 19.
Now everything works fine, but does anybody know what i am missing out, whit this one leg missing?
Its not the keyed pin. It looks like its the chip select and R/W control on PIA 9B which interfaces with the segment displays. Are your displays working correctly? No lines out or decimal points out?
Ok, I'll try to explain. This is just from me looking over the datasheet and your schematics. I'm sure there is a PIA expert out there somewhere. That pin (19) goes to pin 25 on the PIA. This is the E pulse or enable for the chip select. The PIA is on a bus (along with other chips) and its chip select lines are tied...somewhere to the processor.
When the processor idles, those chip select lines will be in some state (doesn't matter what state). There will most likely be noise or something that we don't care about going through those lines. This is where the enable comes into play. When the processor is idle, enable is low or disabled. So the chip selects are in a state but you cannot write to them aka they can't listen. Its sort of a feature that makes it so certain events (like display line or anything else the pia controls) doesn't fire from noise.
I don't feel its a problem but if you closely watch your display (again or whatever the PIA is connected to...i think in your case its the segment displays) they might intermittently mess up.
Great to see you're enjoying Pinside! Did you know Pinside is able to run thanks to donations from our visitors? Please donate to Pinside, support the site and get anext to your username to show for it! Donate to Pinside