Saturday, 8 September 2012


 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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