Rev D
Model MS-500x
CrossPoint Technologies, Inc
5
The interface requires 2 twisted pairs of wires between the communicating devices. Shielding is
recommended over the two pairs. For best performance and safety, do not ground the shield at
both ends. Leave one end of the shield unconnected. If each pair is individually shielded, ground
the shield at its source end (driven end) and leave it floating at its receiving end.
The suggested drawing below is for the RS-422 interface using 2 twisted shielded pairs. The
computer side does not show pin numbers, as there are many forms of RS-422 connectors
available. Notice the individual shields are grounded at opposite ends, and there is no ground
continuity between the two devices (the two shields are assumed isolated from each other). In
long runs, this serves to protect both devices from carrying ground currents, especially in the
event of a power line fault in either device. If your cable has individual shields that are in intimate
contact with each other, it may not be possible to avoid ground current flow down the cable shield.
5
4
3
2
1
9
8
7
6
9 pin female D connector
Computer
RS-485 Connector
TXB
TXA
RXB
RXA
Gnd
TXB
TXA
RXB
RXA
Figure 3 : Computer to Matrix RS-422 Wiring
A standard PC RS-
232 port can be transformed to balanced operation using an “RS-232 to RS-
422” or “RS-232 to RS-485” adapter device. These devices are available from a variety of
sources. Some can be powered directly from the RS-232 handshake signals available at the PC
connector. This type is recommended, as it does not require a separate power supply or
transformer for operation.
Suggested sources for these adapters are B&B Electronics (
www.bb-elec.com
or 815-433-5100
)
and Black Box Network Services (
www.blackbox.com
or 877-877-2269).
