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STAR Line Mode Command Specifications 1-2
1.1.3. Communication Protocol
1) General description of operations in the DTR mode
This mode abides by the DIP switch settings. (Ex-factory settings)
This mode performs communication while handshaking with the DTR signals. In the operations to receive printer data,
this mode controls the DTR signals by confirming the BUSY signal. A SPACE indicates that the printer is ready to
receive data; conversely, a “mark” indicates that the printer cannot receive data.
If there is no printer error after turning ON the power, the DTR signal line is set to a SPACE. When the host computer
confirms that the DTR signal line is a SPACE, it sends the data text to the RXD signal line. The printer sets the DTR
signal line to a “Mark” after the empty area of the data buffer reaches a maximum of 256 bytes. When the host
computer confirms that the DTR signal line is a Mark, it stops the transmission of data text to the printer buffer, but at this
point as well, the printer is still capable of receiving data, up to the amount of empty space in the data buffer. If the host
computer ignores the DTR signal and transmits data, all data exceeding the amount of space in the data buffer is simply
discarded. The printer sets the DTR signal line to SPACE again when the amount of empty space in the data buffer
increased because of the printing and the data in the buffer is a maximum of 256 bytes.
2) Buffer full/Buffer full cancel in the DTR mode
Full Near Full Near Empty Empty
Buffer Empty area: 256 bytes Reception data: 256 bytes
DTR "Mark" DTR "SPACE"
DTR is set to mark at the point the empty area is a maximum of 256 bytes.
DTR is set to SPACE when the data in the buffer is a minimum of 256 bytes.
<When ON-LINE>
RXD DATA DATA DATA
DTR
Printing
Power ON Buffer full Buffer empty
<When out of paper>
RXD OFF-LINE ON-LINE
DTR ON-LINE Recovery
Printing Out of paper
No paper signal
Power ON