USB232U/485Ui
Page 12
Reference Signal Ground
(pin 5 of 9-way) is internally connected to the PC USB signal
ground and should be externally connected to the Signal Ground pin of the RS232
device at the other end of the link.
The
Connector Shell
is internally connected to the PC USB chassis ground. Protective
ground should be externally connected to the protective ground pin of the RS232 device
at the other end of the link. To maintain shield integrity, metal connector hoods should
be used, preferably at both ends. These hoods make contact with the connector shell
and the cable screen so maintaining an overall shield.
3.3.2
USB485Ui Ground Connections
Reference Ground
is internally connected to the isolated signal ground that must be
connected to the signal ground of the remote RS422/485 device. Any voltage appearing
between this reference ground and the host PC USB ground is common mode and must
not exceed the isolation voltage.
Connector Shell
is not connected. To maintain shield integrity, a metal connector hood
should be used which must be connected to the cable screen at the remote device.
3.4
Choice of Cable
As speeds and distances of communication increase the choice of cable over which the
communication is to take place becomes critical.
Amplicon recommend Belden Cable, part no. 8132 for use in long distance high speed
RS422 & RS485 networks.
This is multi-shielded twisted pair cable. It has a capacitance of 20pF/m and
characteristic impedance of 120 ohms.
In order to maintain compliance with the EMC directive, 89/336/EEC, it is strongly
recommended that the final system integrator uses good quality screened cables for
external connections. It is up to the final system integrator to ensure that compliance
with the Directive is maintained. Please contact our sales staff for further information.
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