Star Micronics SP300 - Manual (Page 20)

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[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.
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.
TXD
RXD
ON
OFF
X–ON X–OFF X–OFF X–ON X–OFF X–OFF
X–OFF
X–ON
X–OFF
Printing
Paper out
signal
ON LINE
lamp
Data Data Data
Paper out Power ON Load paper and press
the ON LINE switch.