RS 232 SERIAL COMMUNICATION
RS232 is a popular communications protocol for connecting modems and data acquisition devices to computers. RS232 devices can be plugged straight into the computer's serial port (also known as the COM or Comms port). Examples of data acquisition devices include GPS receivers, electronic balances, data loggers, temperature interfaces and other measurement instruments. A nine pin D plug has become the standard fitting for the serial ports of PCs. The pin connections used are as shown in Table 4. The connector on the PC has male pins, therefore the mating cable needs to terminate in a DB9/F (Female pin) connector
RS232 PIN ASSIGNMENTS (DB9 PC SIGNAL SET)
Table 4: RS232 PIN ASSIGNMENTS (DB9 PC SIGNAL SET)
Pin 1
|
Input
|
DCD
|
Data Carrier Detect
|
Pin 2
|
Input
|
RXD
|
Received Data
|
Pin 3
|
Output
|
TXD
|
Transmitted Data
|
Pin 4
|
Output
|
DTR
|
Data Terminal Ready
|
Pin 5
|
Signal Ground
|
||
Pin 6
|
Input
|
DSR
|
Data Set Ready
|
Pin 7
|
Output
|
RTS
|
Request To Send
|
Pin 8
|
Input
|
CTS
|
Clear To Send
|
Pin 9
|
Input
|
RI
|
Ring Indicator
|
Normal PC hardware
might well run with just Tx, Rx and Ground connected, most
driver software will wait forever for one of the handshaking lines to go to the
correct level. Depending on the signal state it might sometimes work, other
times it might not. The reliable solution is to loop back the handshake lines
if they are not used.
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