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SurePOS 100 Technical Reference
Page 32 of 104
Figure 3-5. DTR Signal Timing
If a printer logic board error does not occur after the power is switched ON, the DTR signal line is asserted.
After the application confirms that DTR is asserted, the application program can send data to the printer at any
time. The printer logic drops the DTR signal when the empty space in the data buffer is below 256 bytes. After the
application detects that the DTR signal has dropped, transmission of data must stop. In DOS and OS/2 systems,
this buffer management can be completely handled by the operating system. No application programming is
required to implement this handshaking.
When the data in the data buffer is reduced to 256 bytes or less, the empty space in the data buffer is increased
and the printer logic asserts DTR. Then the printer is ready to receive more data.
Figure 3-6. DTR Data Buffer
9.3.1.1 Framing Error
A framing error occurs when space is detected at the stop bit. When a framing error or parity error
occurs for the data that is received, the printer prints out a "?" mark to indicate that the error occurred.