Whilst waiting for physical stuff to arrive, I have also started looking into this printer. As typical for things on eBay, you frequently don't get a data sheet with the item. This is listed as 'Aps Elm203-CH' compatible, so I'll try to dig that data up from somewhere.

In the meantime, it seems that this will probably be ESC/POS compatible from a command set standpoint (this is a common POS printer command set), so there will need to be some translation of the HP commands to ESC/POS. This shouldn't be too hard. What will possibly be more 'interesting' is that this printer has a different character set than the HP82240A/B, so I might wind up operating it in graphics mode and rasterize the text mode output myself. Hopefully I will have the RAM for that, but I think I probably will.

Another challenge is that the resolution of this printer is higher and incompatible with the HP82240 unit. This printer has 384 dots per line, and the 82240 has 166(?). So, even doubling the pix will still be 52 short, which is about 13%. I'll need to do some thinking and experimentation to see what looks best: discarding the extra 52, or stuffing dups in.

Lastly, the Devil is in the details, and sometimes items on eBay indicate something that is not entirely true. This is listed as serial RS232/TTL, which I hope is an accurate statement. The serial is a must in order for me to be able to use the BluePill board, and the TTL is important to avoid extra parts. And I hope 3.3V logic, but the pins should be 5V tolerant, I think....