User`s guide

Page 97

Controlinc 1746-C (Version 5.21) Network Master Users Guide (2004-11-18)

6.2.5. Communication Failure Indications (Low-Level & High-Level)

Only low-level communication problems flagged as errors in tables [1 & 2].

“Modbus exception messages” are high-level (application level) communication errors. These are

logged in table [20].

Both types of communication errors are cleared only at the beginning of a diagnostic scan.

The 1746-C has 3 mechanisms for reporting communication problems:

1. Table [1]: (low level) The values 0- 3 such that:

• 0  No problems on any port (same as table [2] – bit-14 = 0)

• 1  Problems on Port 1 (may be used to assist diagnostics)

• 2  Problems on Port 2 (may be used to assist diagnostics)

• 3  Problems on both ports … general communication fault.

(

same as table [2] – bit-14 = 1)

2. Table [2]: (low level) Bit 14 such that:

• Bit-14 = 0: Communication OK (same as table [1] = 0)

• Bit-14 = 1: General communication fault (same as table [1] = 3)

3. Table [20]: (high level) Modbus Exception Indicators sent from the actuators.

Notes:

• Diagnostic communication error indications for problems on port 1 or port 2 are flagged anytime

a transmission is attempted and fails on a particular port.

If an actuator is already flagged as having a problem on one port, then the program will only try

using the other port (until the next diagnostic scan). If a problem also exists on the 2

port,

then a general communication fault exists.

• General communication faults (Table [1] == 3) and (Table [1] – bit-14 == 1) are flagged when a

message fails to successfully transmit.

• If an actuator is already flagged as having a general communication fault (can’t communicate on

either port) then the program will not attempt to transmit on either port (until the next diagnostic

scan).

To truly understand the meaning of the values in Table [1] and the 1746-C’s behavior on the network,

you must know the physical layout of the network and exactly how it was wired.

For instance, at the actuators, you must know if the wiring is actually coming in from NIU-port A into

port A in the actuator and out port B … (and into the next actuator in port A and out port B … … …).

Actual “as built” diagrams from the electrical contractors often help here.