Chapter1
Motherboard Description
1-20
signals to initiate communication. If you encounter a communication problem that
cannot be resolved using a null modem, it can generally be assumed that one
device is using the initialization signals and the other device is not. This can
usually be resolved by wiring the RTS, CTS, and DCD pins together.
Serial Ports/COM Ports
The two serial ports on the computer are called COM1 and COM2, respectively.
If you wish, two more serial ports can be added onto the computer using optional
hardware. Should you choose to add the extra Serial ports (COM ports) they
would be called COM3 and COM4.
When using serial ports to communicate with a peripheral device, be sure to
assign only one COM port number to each device. For example, if a printer and a
scanner are both connected to your computer through serial ports, the printer must
be assigned one COM port (i.e. COM1) and the scanner must be assigned the
other COM port (i.e. COM2). No two devices can be assigned to one COM port.
Each peripheral must have its own COM port.
NOTE: Four serial ports may be installed on the computer. However, no more
than two ports can be used simultaneously.
*If you have installed an internal modem, be careful not to assign a COM port
number that has already been assigned to another device. This error is common.
When installing a device that is going to require the use of a serial port, use a
diagnostic program to find out which ports are available. It may be necessary to
remove expansion cards that have serial ports in order to check their jumper
settings. The jumper settings will indicate which COM port the card has been
assigned. Checking the expansion card will eliminate mistakes in overlapping
COM ports. Once you have completed the installation of peripheral devices using
the serial ports, be sure that the communication parameters such as baud rate,
parity bit, etc. are matching. If your computer is set for a baud rate of 9600 and
your modem is set for a baud rate of 2400 you will not be able to send messages.
The manuals that accompany the peripheral devices will inform you on the
procedure for setting their parameters. Software manuals also have instructions on
setting parameters.
