X-On/X-Off Mode - Star Micronics DP8340 Series User Manual

9-2. X-ON/X-OFF Mode

The printer transmits an X-ON (Control Code; DC1, Hexadecimal Value; 11H,)
signal after power is turned on, if there is no printer error being generated.
When this signal is received by the host computer, the host computer transmits
the data to the printer. The X-ON signal is output intermittently every three
seconds until the host computer receives and responds to this signal.
The X-OFF (DC3, 13H) signal outputting begins when the amount of empty
space in the buffer becomes less than 256 bytes. When the computer receives
the X-OFF signal, it will halt data transmission as soon as it can. However even
at this time the printer can receive data until the buffer is completely full. An
X-ON signal is output when the contents of the buffer goes below 256 bytes.
The increase of the empty area in the buffer is caused by printing. If the computer
causes a buffer overflow, a flag bit in the status register will be set. (See Status)
The X-OFF signal will continue to be output at a 3-second interval until the
data buffer becomes near empty (less than 256 bytes).
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