Hardware Reference
In-Depth Information
Figure 14.24. Standard 25-pin serial port connector specifications.
Serial ports were once used to connect printers and external modems, but in modern Home Theater
PCs they are used to connect infrared transceivers to allow for remote control operation.
The official specification recommends a maximum cable length of 50 feet. The limiting factor is the
total load capacitance of cable and input circuits of the interface. The maximum capacitance is
specified as 2,500pF (picofarads). Special low-capacitance cables can effectively increase the
maximum cable length greatly, to as much as 500 feet or more. Also available are line drivers
(amplifier/repeaters) that can extend cable length even further.
Tables 14.11
,
14.12
, and
14.13
show the pinouts of the 9-pin serial connector, the 25-pin serial
connector, and the 9-pin-to-25-pin serial adapter, respectively.
