08-02-2022, 09:00 AM (This post was last modified: 08-02-2022, 09:00 AM by nauseous.)
OK, I assume that is exactly what I am looking at here (ETI680 ROM).
The other two PROMS where located at the bottom end of address space, the "DGOS 1.4 c1980" PROM was located at 6000h.
So question here; I can't find a photo of an ETI680 card, but did it have the ROM onboard?
Yours has quite a few odd mods. Can you post a more detailed close up photo of it?
Someone'd stay with DGOS 1.4 as its the best for getting things going.
It's designed to work with just a DG680 CPU and DG640 VDU installed so start with that configuration first.
If using the DG0S 1.4 - ensure that the POJ DIP switches are set correctly to %D000.
It appears you're missing an IC38 (74LS139) to the right near the Z80 CTC - make sure that this installed.
It is also advisable to wind down the CPU oscillator to 2MHz at first.
What IC is inserted at position 26? It should be a 74S200 or equivalent - these have always been rare and expensive.
(Note: DGOS 1.4 will work just fine without a 74S200 installed.)
If things are really pear, then see if you can get some 2716 (single voltage) EPROMs and write your own diagnostic boot ROMs.
e.g. Write a single byte in a ROM with %76 (Halt Instruction) to turn on the HALT LED.
Sorry, but this is not my DG680 board but a pic I acquired recently. I'm hoping the ACMS will obtain the unit and I will then be able to get a better picture.
