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10
V550-A20 Operation Manual
Section
5-
10
Appendices
Protocols Used With RS-232 and RS-422
RTS/CTS (Used with only RS-232)
This protocol stands for "Request To Send" and "Clear To Send". This
is a common type of "handshaking" that goes on between two units.
When one device wants to transmit to another device, it will drive the
RTS line indicating it has data to transmit. When the receiving device
is ready to receive, it will drive the CTS line indicating it is ready.
When you use RTS/CTS it requires the addition of two more wires on
the communication cable. If they are not needed then it is advised not
to use any other additional lines in the cable.
ACK/NAK
This is a software protocol. When a unit receives a message, it indi-
cates whether it has received that message correctly. If all informa-
tion is received, the unit will transmit an "ACK" (acknowledge). The
ACK is a signal that more information may be transmitted. If the
information is not received correctly, then it will transmit a "NAK"
(non-acknowledge). The NAK is a signal requesting a message be
retransmitted. Most software has a limit to the number of retransmits.
Three NAKS is common.
XON/XOFF
This is a software protocol. XON stands for "transmit on" and XOFF
stands for "transmit off." A unit receiving data may signal the unit
transmitting that it should stop sending data by transmitting and
XOFF (ctrl-S). An XON (ctrl-Q) signals the original unit to begin
transmitting again.
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