Epson TM-T20 Technical Reference Manual page 83

Functions of each connector pin
Pin no. Signal name
2 RXD
3 TXD
4 DTR
5 SG
6 DSR
7 RTS
Signal direction
Input Reception data
Output Transmission data
Output 1) When DTR/DSR control is selected, this signal
indicates whether the printer is BUSY.
• SPACE status
Indicates that the printer is ready to receive data.
• MARK status
Indicates that the printer is BUSY. Set BUSY conditions
with the memory switch.
2) When XON/XOFF control is selected, the signal
indicates that the printer is properly connected and
ready to receive data from the host. The signal is
always SPACE, except in the following cases:
• During the period from when power is turned on to
when the printer is ready to receive data.
• During the self-test.
— Signal ground
Input This signal indicates whether the host computer can
receive data.
SPACE indicates that the host computer can receive
data. MARK indicates that the host computer
cannot receive data.
When DTR/DSR control is selected, the printer
transmits data after confirming this signal (except if
transmitted using some ESC/POS commands).
When XON/XOFF control is selected, the printer does
not check this signal.
Output Equivalent to DTR signal (pin 4)
Appendix
Function
83