Epson TM U200D - B/W Dot-matrix Printer Technical Manual page 150

If the electric potential of CS1 is higher than that of CS2, the TM series printers are ready for
communication (the host is ready to receive data). If the electric potential of CS1 is lower than
that of CS2, the TM series printers are not ready for communication (the host is not ready to
receive data).
DR1 DR2
H L
L H
If the electric potential of DR1 is higher than that of DR2, the TM series printers are ready for
communication (the host is ready to receive data). If the electric potential of DR1 is lower than
that of DR2, the TM series printers are not ready for communication (the host is not ready to
receive data).
Appendix A-2
Communication is available
Communication is not available
Function
Rev. B