North Star Z-80A ZPB-A2 with original PROM option

[haglebu]

The following NS Z-80A card features the original PROM option and a PROM and POJ address to F000h.

So far I have only copied the EPROM (see attachment) and made a test with Dave Dunfield's Horizon Emulator. The address F000h in the PROM is correctly accessed, but then the message "Unkown I/O Port" appears and that's it.

The label on the EPROM reads:

NS BOOT 60
F000
870315





I would be pleased to receive further information.

 

[Hugo Holden]

That board looks to be in pretty good original order.

It does contain a number of TI brand IC's and sockets, which can have a propensity for corrosion on their pins.

I would start by cleaning up the IC pins and cleaning/checking the sockets, just to make sure all of the connections were sound.

Also I would check those jumper connections and make sure they were correct.

I'm not sure how an emulator would help you here, and just the ROM contents alone, because it throws in some unknowns.

To check the pcb operation and integrity of the ROM, it might be better to run it up in a real S-100 computer.

 

[haglebu]

I have another working ZPB-A2 board, also with the original PROM option (2708). I changed 2E, 5E and the EPROM and ... the board is working flawlessly.

Next I used a real N* Horizon; this shows exact the same message as the emulator ... and then it stops. I used a HRAM64 and MDS-AD3 with my DREM; this configuration is working properly.



I have no information about which address this "870315" ROM jumps to. Normally it would be the E800h, at least for the MDS-AD N* FDC.

 

[Hugo Holden]

Maybe it was once in a system with an MDS-AD3 card or other FDC, where that had a modified ROM, so the MDS FDC card responded at F000h, rather than E800h. It could be a puzzle. Also it is possible the ROM might be corrupt. I have seen some MDS cards with modified ROMs on them to other addresses.

 

[deramp5113]

After a quick look at the PROM content, it appears to be a boot ROM for a double density floppy drive, however, it’s not one of the normal NS controllers. This PROM is using an I/O mapped controller instead of the memory mapped NS controllers. It also appears it may be a smart controller that uses DMA.

Mike D

 

[haglebu]

Thank you very much Mike. I thought something like that, because the designation of the EPROM "87" is probably 1987 and possibly refers to a controller with a more recent date. In 1987, IBM PCs were already at their peak.