Hardware Handshaking - Symbol LS 1220 Product Reference Manual

Hardware Handshaking

Hardware Handshaking allows a check of the host the readiness before transmitting data.
If the host is periodically occupied with other tasks, Hardware Handshaking is needed to
prevent loss of transmitted data. Refer to the Hardware Handshaking diagram, Figure 8-1.
RS-232C communications are designed to operate either with or without hardware
handshaking lines - Request to Send (RTS), and Clear to Send (CTS).
If RTS/CTS handshaking is selected, scan data is transmitted with the following sequence
(Note that the DTR signal is hard wired active):
1. The scanner (LS 1220) reads the CTS line for activity. If CTS is asserted, the
scanner waits up to 2 seconds for the host to negate the CTS line. If, after 2
seconds the CTS line is still asserted, the scanner sounds a transmit error (if
equipped with optional beeper), and any scanned data is lost.
2. When the CTS line is negated, the scanner asserts the RTS line and waits 2
seconds for the host to assert CTS. When the host asserts CTS, data is
transmitted. If, after 2 seconds the CTS line is still not asserted, the scanner
sounds a transmit error (if equipped with optional beeper), and any scanned data
is lost.
3. When data transmission is complete, the scanner negates RTS 10 msec after
sending the last character.
4. The host should respond by negating CTS. The scanner checks for a negated CTS
upon the next transmission of data.
During the transmission of data, the CTS line should be asserted.
If the above communications sequence fails, the scanner issues a transmit error. In this
case, the data is lost and must be rescanned.
If no Hardware Handshaking is selected, data is transmitted based on the Software
Handshaking options which follow.
Programming
8-13