Hardware Handshaking - Motorola LI4278 Product Reference Manual

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 scanner reads the CTS line for activity. If CTS is asserted, the linear imager scanner
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 scanner sounds a transmit error, and
any scanned data is lost.
•
When the CTS line is de-asserted, the linear imager scanner 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 scanner sounds a
transmit error, and discards the data.
•
When data transmission is complete, the linear imager scanner de-asserts RTS 10 msec after sending
the last character.
•
The host should respond by negating CTS. The linear imager scanner 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 scanner sounds a transmission error, and
the data is discarded.
If the above communication sequence fails, the linear imager scanner 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.
RS-232 INTERFACE 7 - 11