RS-232 INTERFACE 4 - 11
Hardware Handshaking
The data interface consists of an RS-232 port designed to operate either with or without the hardware
handshaking lines, Request to Send (RTS), and Clear to Send (CTS).
If Standard RTS/CTS handshaking is not selected, scan data is transmitted as it becomes available. If
Standard RTS/CTS handshaking is selected, scan data is transmitted according to the following sequence:
•
The linear imager reads the CTS line for activity. If CTS is asserted, the linear imager waits up to Host
Serial Response Time-out for the host to de-assert the CTS line. If, after Host Serial Response Time-out,
the CTS line is still asserted, the linear imager sounds a transmit error, and any scanned data is lost.
•
When the CTS line is de-asserted, the linear imager asserts the RTS line and waits up to Host Serial
Response Time-out for the host to assert CTS. When the host asserts CTS, data is transmitted. If, after
Host Serial Response Time-out, the CTS line is not asserted, the linear imager sounds a transmit error,
and discards the data.
•
When data transmission is complete, the linear imager de-asserts RTS 10 msec after sending the last
character.
•
The host should respond by negating CTS. The linear imager checks for a de-asserted CTS upon the
next transmission of data.
During the transmission of data, the CTS line should be asserted. If CTS is de-asserted for more than 50 ms
between characters, the transmission is aborted, the linear imager sounds a transmission error, and the data is
discarded.
If the above communication sequence fails, the linear imager issues an error indication. In this case, the data is
lost and must be rescanned.
If Hardware Handshaking and Software Handshaking are both enabled, Hardware Handshaking takes
precedence.
NOTE The DTR signal is jumpered to the active state.
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