Datamax E-Class Mark II Programmer's Manual page 279

Appendix J – General Purpose Input Output Port Applications
Pin 3 should be pulled to +5VDC. In additional,
connections for the external Start of Print control can
either be directly made to Pin 4 of the Option Port (or
Main PCB connector) using a TTL-level input, or via an
interface circuit (similar to the one shown). For more
information, see the table below.
Class Series 2 Programmer's Manual
MII Sample SOP Circuit
GPIO Connector Pin Number
Vcc 1
Spare 3
SOP 4
Gnd 8
1K O
1K O
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