Citizen iDP-3550 - Page 45

(8) RCH
When the printer is ready to receive, this signal is turned to Space. This signal line is the same as
DTR.
(9) mTXD
TXD signal for the diode gate.
(10) mRXD
RXD signal for the diode gate.
(11) FG
This is a Frame Ground signal.
(12) GND
This is a common ground on the circuit.