You're right, the paper was different, I forgot that.
The Alphacom was a driven by the edge connector, like the Timex Sinclair. Nothing fancy like RS232.
IIRC whole lines were sent by an OUT to some port (forget which one, but there weren't many). Each line was 256 pixels long, the Spectrum sent the bitmap for the first row of pixels (32 bytes), then the second row of pixels, and so on down to the eighth. I can't remember if a linefeed was a code or just 8 empty rows.
If you can get hold of The Complete Spectrum ROM Disassembly that will show you the printer driver code.
Biting the hand that feeds IT
