BEWATOR COTAG 4101-2, Installation Handbook, Page: 144 / 158

4101-2 Controller Installation Handbook
19-12
Is the PC Com port OK?
The system will normally run connected to COM1: on the PC. There is
sometimes a need to use COM2: if the PC is using COM1: for some
other purpose, such as a mouse.
If a serial mouse is installed, or has in the past been installed, check
whether the mouse driver is using the same COM: port that the
system is plugged into. If it is, either move the mouse driver to
another port (see instructions provided with mouse) or move the
system to another port. We recommend you use a bus mouse which
prevents the problem occuring in the first place.
To communicate with the local Controllers via COM2:, click on the
Local Comms button on System Manager’s Configuration page and
choose COM2.
If the PC COM port is still suspected you should use an RS232
checker (little plug/socket unit with LEDs) to see if the TXD line is
being polled by the PC.
Is the RS232/RS485 Selection OK?
When a 4101 Controller is talking direct to the PC it must have SW3-
4 in the up position. When controllers are connected to a Comms
module SW3-4 must be in the down position. (Remember to remove
and restore power to the controller if you change a switch setting so
the microprocessor will read the switch setting.)
Are the cables too long?
The maximum specified distance for an RS232 connection is 15
metres. Greater distances may work when using screened cable but
noise can affect the communications.
The maximum specified distance for the RS485 cable is 1km. This
must not be exceeded. If necessary, use a Comms module in
operating mode E to restore the signal conditions. See chapter on
Comms modules for more information.
Checking the RS232 connections at the PC
Refer to the connection diagrams in the chapter on the 4101 Modular
Controller and check each one carefully. Points to check are:
•
Correct cross-over of TXD to RXD.
•
CTS and RTS linked together at the PC end and not connected
to the controller end via the RS232 cable. (If CTS and RTS are
not linked at the PC the comms may work intermittently!)