Star Micronics SP300 Series - Manual (Page 18)

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2-6. Data Structure
2-6-1. DTR mode
This mode is accessed when the DIP switch 3-5 is ON.
Signals are controlled using the DTR line as BUSY flag.
If a printer errors do not occur after the power is turned on, the DTR signal line
changes to “SPACE”.
When the host computer confirms that the DTR signal line is set to “SPACE”, the
host computer sends the data text via the RXD signal line to the printer. Also, the
printer will set the DTR signal line to “MARK” when the empty space in the data
buffer is below 256 bytes. After the host computer detects that the DTR signal line
is at “MARK”, transmission of the data text is sopped. In this instance, data can
still be received up until the data buffer becomes completely full.
When the empty space in the data buffer is increased following printing (when the
data in the data buffer is reduced to 256 bytes or less), the printer sets the DTR
signal line to “SPACE”.
RXD
DTR
Data Data Data
Buffer full Buffer empty
Printing
Power ON
RXD
DTR
OFF LINE ON LINE
When paper is out
Printing
PAPER OUT signal
Power ON
Paper out
Press the ON LINE switch after
loading paper.