Technical information

What To Do First Serial Solutions
light permits the flow of traffic. Thus a serial port can turn its
output signals on or off to indicate to the external device
whether data can be received or not. It can use its input signals
to sense if the external device is ready to receive more data.
If traffic lights are ignored then crashes will occur. If
handshake lines are ignored data will be sent at the wrong time.
If the traffic lights are misread then no traffic at all might
flow if a green light is misread as a red light. If handshake lines
are misread then serial ports might appear to lock up with no
data flowing in or out.
Serial ports have up to 8 signal lines plus a ground line.
The number of devices connected together using the one stretch
of cable also effects the type of handshake used.
RS232 Handshake Lines.______________________
RS232 ports, fitted to virtually all PCs as standard, use 8
signal lines. The RS232 standard is ancient in computer industry
terms, introduced in 1962 it is now widely established. It is a
slow speed, short distance, single ended transmission system (ie
only one wire per signal). Typically RS232 maximum cable
length is 50 feet with a maximum data rate of 20K bits per
second. RS232 is for data transmitted between only one device
and one other.
The original PC’s RS232 port was a 25 way D type connector
but now PC’s usually have a 9pin D type connector.
Chapter 1 Page 11