Ampro Little Board 186 and mystery piggyback board

[smbaker]

I picked up this set of Ampro boards a little while back. The first is clearly a "little board 186" and the second is a piggyback board that I don't know what it does. The piggyback board plugs into the 80186 socket and relocates the 80186. It has a 26-pin connector. As far as I can tell, not floppy, SCSI, or other device was plugged into this. The two ROMs marked U9 and U10 are not the typicaly Ampro BIOS, but each only hold less than 512 bytes. A few questions:

1) Does anyone have known-good ROMs for this board? http://www.retroarchive.org/maslin/roms has a couple roms marked "Ampro Little Board BIOS" but they're marked U15 and U16, which I tried and did not work. Mine are U9 and U10. There's also a couple other roms marked 75515 and 75516 that I have not tried. A board I saw a picture of on eBay that looks mostly like mine has roms marked 75613 and 75614.

2) Any idea what the piggyback board is for? There are no controller chips on it. There are four 75175 drivers near the 26-pin connector. It has an Ampro logo on it, so likely not something custom.

Thanks,
Scott

 

[GiGaBiTe]

The daughterboard is latching and buffering the address/data buses and has a bit of memory on U10. With the 75175 line drivers, I'd suspect it is some sort of serial card.

 

[smbaker]

I had Claude Code disassemble and analyze the two ROMs. It seems what's there is a loop that continuously reads 17-byte packets from the piggyback board and streams them out the little board's serial port. Claude couldn't give me more specifics without me spending some time reverse engineering the board, but we speculated that it's multiplexing the 16 serial channels of the 75175s to form up these 17-byte packets. Maybe adding a header byte or a checksum or similar. Makes me wonder if this was some kind of logic analyzer or protocol analyer or similar machine.

What I haven't had any success doing is finding a plain ordinary Ampro BIOS that will work in it. The ones at http://www.retroarchive.org/maslin/roms I'm not seeing any output on the serial port, and I would expect at least a banner.

 

[smbaker]

I got the thing workig with the ROMs at http://www.retroarchive.org/maslin/roms. Turns out there is no banner emitted on startup, and there is no message emitted if the floppy (or SCSI) is unable to boot. The board is silent. I ended up removing the piggyback board and moving the CPU to the main board, and I had to clean the corrosion off of the floppy connector. Then it just takes about 30 seconds of patience with a properly-connected floppy drive to get DOS 2.10. to boot.