Handshaking - Husky MP2500 Manual

13.5.1 Handshaking

While you do not need to know how handshaking works in order to use
MP2500 communications, you may find the following of interest.
Handshaking is a form of control provided by adding extra wires between
the two communicating systems. These allow the two systems to
communicate information such as 'I am ready to transmit' or 'I am ready for
another character'.
Each handshaking signal is carried by a different wire and has a different
name (CTS, RTS, DTR, etc). These names are often used interchangeably
for the signal and for the wire or pin carrying it.
Port 1 (COM2) includes a number of handshaking lines which conform to
the standard RS232 specification for use with modems, and may be
configured to suit particular requirements.
Handshaking is usually used when operating with a modem, but may also
be used when communicating with slow devices (such as printers) which
are connected direct to the MP2500, or to allow the MP2500 to suspend
data transmissions to it.
As handshaking involves extra wires, it cannot be used over normal
telephone lines, to control the remote system. Instead, handshaking is used
to control the modem which connects the MP2500 to the telephone line. (A
control mechanism similar to handshaking can be achieved by using a
protocol, which includes control messages with the data being transmitted.
See section 13.5.2.)
You can change the way the MP2500 produces and reacts to handshaking
signals from applications or the UTIL utility. This makes communications
rather easier than with systems which have fixed handshaking (with these,
you often need to produce custom cables to 'trick' handshaking).
The individual handshaking lines are described in turn later in this chapter,
with the single exception of Ring Indicator (RI). RI is an input which will turn
the MP2500 on. It is often used by an auto-answer modem, to turn the
MP2500 on when a call is received so it can process the call.
Chapter 13: Introduction to Communications 125