Amiga 1000 ROM question

[cbmeeks]

So while debugging my A1000's faulty (EVEN) ROM chip, I decided to try and replace it with a AT28C64. Which is a 8 KiB chip. Granted, the original 23256 is 32 KiB, only 8 KiB is actually used.


From what I understand, the 23356 is pin compatible with a 27256. I have ordered a couple Intel 27256's. But in the meantime, I don't see why I can't get the AT28C64 to work.


Regarding the pins, there are only two pins that conflict. Those are pins 26 and 27. Which, on the Amiga, maps to A14 and A15.


The AT28C64 doesn't have A14/15. Those pins are actually a NC and /WE. So my thinking was to lift those two pins and wire the /WE to 5V.


I tried this and all I got is a black screen. When I put the faulty EVEN ROM back in, I get my orange color again.


So my question is, anyone know why this wouldn't work?


Also, one thing I noticed is that on the A1000 schematic, the 23256 refers to the output enable pin as "OE" instead of "/OE" like the AT28C64 and the 23256 datasheet do. I assume that's just a poor label on the (crappy) schematics. I can't imagine I would need to invert those signals.


Any help is appreciated.


Thanks!



**UPDATE**

I must have done something wrong. Or maybe the chip was bad. I burned another one and tied /WE high and now I get the same effect as the original mask ROM.

Which is an orange screen. Running out of ideas on this repair. :-(

[indigolemon]

Have you tried Diagrom? https://www.diagrom.com/

There is a set of files in there for the A1k, should give you basic diagnostic output from the serial port if the graphics aren't happy (check your wiring here, the A1000 has gender swapped serial/parallel ports to other Amigas).

[TjLaZer]

Diagrom is a replacement Kickstart ROM, the A1000 doesn't use Kickstart in ROM. It uses Kick boot ROMS which are 8k each. An adaptor is needed to install a Kickstart ROM.

[Jope]

There is a subset of diagrom that can be burned in place of the bootstrap roms.

[indigolemon]

What Jope said. It's not as full featured as Diagram proper, but might give some clues.

[cbmeeks]

Thanks for the replies. I will be trying out the diagrom hopefully today.
I ordered a couple of Intel P27256-25 EPROM's that should be arriving today. Hopefully, they will work and my programmer will correctly handle them.

[TjLaZer]

Did anybody ever figure out how to easily add the third and fourth ROMs to give it a proper kickstart in ROM? I know c= used to offer this as a dealer or developer add on.

[cbmeeks]

I'm getting so annoyed at this programmer. So I got the two Intel P27256's in today. First thing I did was attempt to read the chips. Worked just fine. Then, I decided to program them with a test pattern. Such as "42". Worked fine.

Now, I can't program anything else other than "42" to all bytes. If I change it to 50, then it says 50 doesn't match 42 so it stops with an error.

Somehow, not sure how, but somehow, I managed to change the first byte to 00. But now, I can only program it with what's already on the chip. Surely these aren't one time programming.

But seeing that I cannot erase the chip, I'm thinking I really messed up. However, sometimes it fails with programming modern EEPROMS that I know work.

Ugh.

UPDATE:

Well, looks like I can program all 00's all I want. Anything else fails.

[Jope]

Originally Posted by TjLaZer

Did anybody ever figure out how to easily add the third and fourth ROMs to give it a proper kickstart in ROM? I know c= used to offer this as a dealer or developer add on.

https://bigbookofamigahardware.com/b...t.aspx?id=1842

The PAL contents are not available though.

Seems it will only support a 256k kick in the four sockets, so perhaps a 68000 socket ROM board is the best approach in any case.