The printer port supports one-directional 7bit data, strobe, and busy signals.
Data / Strobe
Port EFXX - Printer Port Output 74LS273 (7bit Data and Strobe) (W)
Bit 0-6 Printer Data (7bit) (0=Low, 1=High) Bit 7 Printer Strobe (0=High, 1=Low)
Busy (PIO.PortB.Bit6)
Port F5XX PIO Port B
Bit 0 VSYNC CRTC Vsync flag (1=VSYNC active) Bit 1-3 LK1-3 Distributor Code (see below) Bit 4 LK4 Desired Screen Refresh Rate (0=60Hz, 1=50Hz) (see below) Bit 5 /EXP External Input (used for external hardware only) Bit 6 BUSY Printer Busy flag (1=Busy, 0=Ready) Bit 7 RD DATA Tape Data Input