User`s guide

Page 71

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

5.4.12. Table [14]: Additional Register Being Polled From Entire Network

Words [4  63] PLC access: Read / Write

This operation allows the operator the chance to poll the entire network for any particular holding

Modbus read command when the particular actuator is being polled (scanned).

This table is not polled for unless the 1746-C is configured to allow it …

• Table [0] – Word [10] … contains the register number to poll for.

• Table [0] – Word [10] … is a flag that indicates whether or not to start requesting that register

from the actuators when scanning such that …

o if Table [0] – Word [11] == 0: The register is not polled (the default).

o if Table [0] – Word [11] =/= 0: The register information is requested when actuators are

polled.

The PLC may reset this table with any value is prefers. To do this, the PLC must insert the new value

into the table and send it to the 1746-C as a write command. The values in this table are not sent out

to the actuators on the network.

A read back of Table [14] will

• If a write command issued: reflect the write command accepted by the 1746-C

• If a read command issued: reflect the last known values of the specified register polled in the

actuators.

If the PLC is utilizing table [14], it is recommended that the PLC also poll table [20]. If an exception

message is returned, then the value won’t be inserted into table [14] but the exception message

indicator will be inserted into table [20].

If detected, and the PLC wants to try again, it should initialize table [14] to some known value and either

explicitly clear table [20] or wait until after the next diagnostic scan (which automatically clears table

[20]) before trying again.

Example Scenario: If there are multiple types of EIM equipment on the network and the table [14]

command requests data from an actuator that is “not supported by that type of actuator” (but is on the

others), the actuator will return a Modbus Exception for that message and the values will NOT be

loaded into tables [14 or 15]. However, the exception codes will be loaded into table [20].

For example, if requesting register [1010] from a

• 320A system … an exception code is returned.

• TEC2000 system … the register containing coils [1069 – 1111] is returned.