Epson SQ-B50/2550 Technical Manual page 37

Table 1-11. RS-232C Serial Interface Connector Pin Assignments
REV.-A
Pin No. Signal Dir.
Description
2
TXD 0 Transmit data.
20
DTR 0
Indicates when printer is ready to receive data. "MARK"
level indicates printer is not ready to receive data.
11
REV(=2nd RTS) 0 Same as DTR.
3 RXD I Receive data.
7 SIGNAL GND
-
Signal (Logic) ground level.
1 CHASSIS GND
-
Printer chassis ground.
NOTE: "Direction" of signal flow is as viewed from the printer.
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