JO-PC1 Base Controller Mounting and Wiring Guide
Updated: January 16, 2012
Part Number JO-PC1 rev 1
Wiring Details
RS-485 Biasing
14
•
from RS-485 “-” to Ground.
Notes
•
In general,
only one device
on an RS-485 trunk should be biased. Otherwise, undue loading of the
circuit may result, with fewer devices supported.
•
RS-485 bias resistors are
different
than “termination resistors”, externally installed at the two
physical ends of a daisy-chained RS-485 trunk, across the “+” and “-” terminals. Termination
resistors are typically 100 or 120 ohm value resistors.
•
Whenever termination resistors are used, RS-485 biasing is typically required.
Adding RS-485 Bias
Note
In many cases
you must furnish the required two 2-pin shorting blocks
. They must be the “shorter
style” jumper blocks. Otherwise, tall blocks interfere when reseating the NPM board. Only units
shipped after mid-2011 may include the jumper shorting blocks, positioned on one pin only of both
2-pin jumpers. See
. Earlier units have only the four bare jumper pins.
To add biasing, you must power off the controller and remove some assemblies (including metal shield, NPM
board) to access the base board jumper pins, located behind the RS-485 port. Then you must install two shorting
blocks on these jumper pins. Then you reassemble the unit by remounting the NPM board, hex standoffs, metal
shield, and shield screws.
Warning
Remove all power from the controller before working on the unit. Observe static discharge
precautions (see
“Static Discharge Precautions,”
).
If the controller is already installed or mounted, it is recommended that you remove it first. Then work on a flat,
stable, and well-lit work surface.