X-On/X-Off Mode - Star Micronics SP300 Series Programmer's Manual

[Framing error]
A framing error occurs when SPACE is detected at the stop bit. When a framing
error or a vertical parity error occurs for the data which is received, the printer
prints out a "?" mark to indicate that the error occurred.
[Compulsion switch]
When pin 6 of the peripheral unit drive circuit connector is set "HIGH", status bit
7 becomes "1".

2-6-2. X-ON/X-OFF mode

This mode accessed when the DIP switch 3-5 is OFF.
X–ON
TXD
RXD
Printing
Paper out
signal
ON
ON LINE
lamp
OFF
Power ON
If printer errors do not occur after the power is turned on, the printer outputs an
X-ON (DC1 by control code; 11H by hexadecimal data) signal on the TXD signal
line which sends it to the host computer. When the host computer receives the X-
ON signal, the host computer transmits the data to the RXD signal line for the
printer. If data text is not sent from the host computer (even after transmitting the
X-ON signal to the host computer), the printer outputs an X-ON signal at 3 second
intervals until the printer receives data.
The printer starts outputting an X-OFF (DC3, 13H) signal when the empty space
in the buffer reduces below 256 bytes. When the host computer receives the X-
OFF signal, it halts output of data. (however, the printer can continue receiving
data until the buffer becomes completely full.)
Output of the X-ON signal is resumed when the data in the buffer is printed out
and drops to below 256 bytes.
X–OFF
X–OFF X–OFF
Data
X–OFF
X–ON X–OFF
Data
Paper out
– 16 –
X–OFF X–ON
Data
Load paper and press
the ON LINE switch.