Epson TM-300A Operator's Manual page 50

[Notes] The status to be transmitted is shown in the table below.
•
When the connector is not used, the value of bit 0 is always "1".
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When DTR/DSR control is selected, the printer transmits only 1
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byte after confirming that the host is ready to receive data (DSR
signal is SPACE). If the host computer is not ready to receive
data (DSR signal is MARK), the printer will keep waiting until the
host is ready. When XON/XOFF control is selected, the printer
is transmits only 1 byte without confirming the condition of the
DSR signal.
There may be a time lag between receiving this command and
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transmitting the status, so the user should be aware of this.
[Reference] APPENDIX B Connectors
ESC v
[Name] Transmit printer status
<1B>H<76>H
[Format]
[Description] This command is supported only by the TM-300A/B.
Transmits the current printer status.
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