X-On/X-Off Mode - Star Micronics TSP400 Series Programmer's Manual

4-5-2. X-ON/X-OFF mode

This mode is accessed when DIP switch 1-3 is set to OFF.
X–ON
TXD
RXD
Printing
PAPER OUT
signal
ON
ON LINE
indicator
OFF
Power ON
Immediately after power on (provided that no error occurs), the printer informs
the host that it is ready to receive data by outputting the X-ON signal (control code
DC1; value = 11H) over the TXD line. If necessary the printer repeats the signal
every three seconds until the host begins sending text data over the RXD line.
When the printer's remaining buffer space falls to 256 bytes or less, the printer
begins to output X-OFF signals (DC3, 13H) over the TXD line. The host
responds by halting the data transfer. Note that the printer remains capable of
receiving data until the buffer becomes full.
Available buffer space increases as the printer prints the buffered data. When the
printer has cleared all but the last 256 bytes of data, it again outputs the X-ON
signal.
Data buffer full Nearly full
256 bytes
remaining
Printer outputs
X-OFF.
X–OFF
X–OFF X–OFF X–ON
Data
– 13 –
X–OFF
X–OFF X–OFF
Data
Paper out
Load paper and press
the ON LINE switch.
Nearly empty
256 bytes
X–ON
Data
Empty
Pinter outputs
X-ON.