Interfaces
8-37
XON/XOFF Protocol Timing (RS-232C)
When you select this data flow control protocol, the printer sends an XOFF signal
when it detects the following BUSY conditions:
•
Buffer full
•
Attendance error
•
Printer not in ready state
The following diagram illustrates XON/XOFF Protocol Timing.
Legend:
1
The RTS signal is driven active as long as power is supplied to the printer.
2
The DTR signal becomes active at the completion of initialization.
3
The printer considers data received invalid when DSR is low and discards the data. (This
is conditional depending on the setting of Honor DSR.)
4
After you power on the printer and DTR is active, the printer sends an XON signal to the
computer (DC1 control or X'11'). However, the computer does not need to detect this
initial XON before sending data to the printer, because the printer can be powered on
before the computer or terminal.
5
The printer sends an XOFF signal (DC3 control or X'13') to request that data
transmission end until the buffer clears. About 640 free bytes remain in the buffer at this
time. If the computer continues to send data after the printer sent an XOFF signal, data
could be lost.
6
The printer sends an XON signal to the computer when the buffer space is again
available. The serial interface is ready to receive more data.
RTS
DTR
DSR
XMT
RXD
Receive Data Valid
1
2
4
3
5
6
XON
XOFF
XON
