External 8bit Printer Port from Amstrad Action Issue 38 (November 1988).
This is a rather bizarre 8bit Printer Port solution. Aside from the 8th data bit, it doesn't come up with any other extras: Data is only one-directional, and only Strobe and Busy control signals are implemented.
Compared with the much older single-wire Happy Computer 8bit Printer Mod (1985), the Amstrad Action approach is terribly overcomplicated.