Automated Logic DIAG485, Technical Instructions, Page: 3 / 3

Figure 2. Sample CMnet Configuration
Segment
M
M M M M M M M
M M M M M M M M M
M
D
R T
T
P
Segment
Segment
T T
T
T
M
M
M
M M M M M
M
P
P P
P
P
R
D
D
M
= Module
= REP485
= 120 Ohm
terminators
= DIAG485
= PROT485
= Earth Ground
R
T
D
P
M
Revised 7/24/03 • DIAG485 3 © 2003 Automated Logic Corporation
Diagnosing Network
Problems
Figure 3 explains the meaning of some of the
signals you may see on the DIAG485. The
length of the network segment affects these
displays; on a lengthy segment, fewer LEDs in
each column may be illuminated. Likewise,
on a short segment, more LEDs may be
illuminated.
Figure 3. Reading DIAG485 LED Signals
Net - Net +
Good communications
One terminator missing
Both terminators missing
No terminator, no bias
Off
On
Properly
terminated, no bias
Too many terminators,
or excessive cable length
Adding Bias
The Bias jumper on the DIAG485 board (see
Figure 1) determines whether network bias is
added. Only one DIAG485 per network
segment can have the Bias jumper in place.
The DIAG485 with the Bias jumper should be
placed in the middle of the segment.
Additional DIAG485s with the Bias jumper
removed may be used on a segment for
monitoring the network communications.
Protection
The DIAG485 is protected by an internal solid
state Polyswitch on the CMnet. This
Polyswitch is not replaceable and will reset
itself if the condition that caused the fault
returns to normal.