Information Technology Reference
In-Depth Information
Figure 13.8
Changing port setting and parameters
13.3.3 Simple no-handshaking communications
In this form of communication it is assumed that the receiver can read the received data from
the receive buffer before another character is received. Data is sent from a TD pin connection
of the transmitter and is received in the RD pin connection at the receiver. When a DTE
(such as a computer) connects to another DTE, then the transmit line ( TD ) on one is con-
nected to the receive ( RD ) of the other and vice versa. Figure 13.9 shows the connections
between the nodes.
9-pin
9-pin
9-pin
25-pin
3
3
3
2
TD
RD
TD
RD
TD
RD
TD
RD
2
7
2
7
2
7
3
4
RTS
RTS
RTS
RTS
8
8
8
5
CTS
CTS
CTS
CTS
4
4
4
20
DTR
DTR
DTR
DTR
6
6
6
6
DSR
DSR
DSR
DSR
5
5
5
7
GND
GND
GND
GND
Figure 13.9
RS-232 connections with no hardware handshaking
13.3.4 Software handshaking
There are two ASCII characters that start and stop communications. These are X-ON ( ^S ,
Cntrl-S or ASCII 11) and X-OFF ( ^Q , Cntrl-Q or ASCII 13). When the transmitter receives
an X-OFF character it ceases communications until an X-ON character is sent. This type of
handshaking is normally used when the transmitter and receiver can process data relatively
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