Page
11
Menu 4: Serial Port Configuration
Handshaking
+----+------+-----------------+------+------+------+------+---------+----+----+
|Port|Device| Device | Baud | Word | Stop |Parity|Handshake|LineDrive|
| | Type | Name | Rate | Size | Bits | | |DTR |RTS |
+----+------+-----------------+------+------+------+------+---------+----+----+
| 1 | RS232| Device A | 9600 | 8 | 1 | None | None | HI | HI |
+----+------+-----------------+------+------+------+------+---------+----+----+
Handshaking......................1
Baud Rate........................2
Word Size........................3
Stop Bits........................4
Parity...........................5
RTS Line Driver Inactive State...6
DTR Line Driver Inactive State...7
Select handshaking:
1 For None
2 For Software Handshaking
3 For Hardware Handshaking
Enter Request :
Select 1), from the Serial Port Configuration Menu
for the Handshaking menu,
Default is 'None'
For a simple communication between devices three connected lines are needed: TX, Rx, and Ground.
For the data to be transmitted, both sides have to be clocking the data at the same baud rate. While this
method is sufficient for most applications, it is limited in being able to respond to problems such as the
receiver getting overloaded. This is where serial handshaking can help.
Software Handshaking:
This style uses actual data bytes as control characters. The lines necessary are
TX, Rx, and ground since the control characters are sent over the transmission line like regular data.
The two control characters, XON and XOFF are characters sent by the receiver of the data to halt the
transmitter during communication.
NOTE:
A drawback to this method is also the most important fact to keep in mind. In ASCII
transmissions these character values are non-character values; however, data being transmitted via
binary, it is very likely that these values could be transmitted as data and the transmission would fail.
Hardware Handshaking:
This style uses actual hardware lines. Like the TX and Rx lines, the
RTS/CTS and DTR/DSR lines work together. When a receiver is ready for data, it will assert the RTS
(Request to Send) line. This is then read by the sender at the CTS (Clear to Send) input, indicating it
is clear to send the data. DTR (Data Terminal Ready) and DSR (Data Set Ready) allow the serial port
and the modem to communicate their status. When the modem is ready for data to be sent, it will
assert the DTR line indicating that a connection has been made across the phone line. This is read in
through the DSR line and the modem can begin to send data. The general rule of thumb is that the
DTR/DSR lines are used to indicate that the system is ready for communication where the RTS/CTS
lines are used for individual packets of data.
