VX121P/151P/171P(-QM57)
User’s manual rev.0.0 (Preliminary)
30 of 68
MU-C656.xxxxxxxxxx r.0.0-EN
5.4 Connecting the serial I/O ports.
The Panel PC can be equipped with up to three RS232 serial ports according to
order options .
Refer to the motherboard user’s manual for further information.
•
Shielded cable must be used for the RS232 serial ports. Inside the cabinet the
cables of the serial ports must be kept separate from the power signal cables.
•
If RS485 port is used, cable must be of twisted pair type. The positive signal
must be twisted with the respective negative signal (e.g. D+ with D-). Moreover
if one is not sure that the common mode voltage will remain within the
maximum values allowed of –7V or +12V with respect to GND the GND
reference signal connection must also be made. If there is connection between
distant appliances (e.g. different buildings or even different departments in the
same building) a possible difference of voltage between the earth must be
considered (even momentarily because of faults of disturbances) which might
make a high current circulate in the GND reference signal and consequently
damage the Panel PC or the connected appliance or the connection cable. In
these cases it is recommended to use an external RS422/RS485 insulated
adapter connected to a RS232 port.
Caution
Do not connect or disconnect the cables of the serial ports with the
Panel PC or the external apparatus switched on.
Notice
The maximum length of the RS232 connection is 15m.
5.5 Connecting the shields
The braids (shielding) of the shielded cables have to be connected to the Panel
PC, directly to the metal casings of the serial port connectors. Those metal casing
are connected to the chassis and to the internal earth point. For proper shielding,
for high frequencies, the shield has to be connected at both ends to ground
reference. If the shield is connected to earth on both ends, care must be taken to
avoid circulating currents.
