Star Micronics SCP700 Series Programmer's Manual page 20

18
X-ON/X-OFF mode
This mode is accessed when DIP switch 1-6 is set to OFF.
X–ON
TXD
RXD
Printing
Printer error
Power ON
The output timing conditions for X-ON and X-OFF are set using Memory Switch
4-C. If memory switch 4-C is set to 0 (factory setting), 1 byte is output for the X-
ON signal when switching from Off-line (Printer Busy) to On-line (Printer
Ready), while 1 byte is output for the X-OFF signal when switching from On-line
(Printer Ready) to Off-line (Printer Busy). If Memory Switch 4-C is set to 1, the
X-ON signals are output every three seconds.
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; valve = 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, value = 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. If Memory Switch 4-C is set to 1,
the X-OFF signal is output each time 1 byte of data is received.
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.
* 16 bytes when the buffer size is set to 45 bytes
X–OFF
Bufferfull
Data
X–ON X–OFF
Bufferempty
Data
Error
X–ON
Data
Recovery
Nearly empty
*256 bytes
Pinter outputs
X-ON.
Empty