The [[KC Compact]] uses the /EXP signal (Bit5 of [[8255|PPI]] Port B) as 8th printer bit.
Amstrad CPCs could be rewired to do the same - but that solution wouldn't be actually recommended - PPI Port B is usually configured as INPUT, so usually, /EXP should tend to be HIGH-Z, and so , standard printer software would probably tend to print chr(80h..FFh) instead of (00h..7Fh).
=== 8bit Printer Port in CPC Plus ===