Input and Output Signals
Publication
PUB091-004-00_0918
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Code 05 and 15 - Force Single Coil or Multiple Coils
The output coils are the discrete outputs from the actuator or its digital
control commands. Code 05 writes one coil per message while code
15 can write values to several at once.
Code 06 and 16 - Preset Single Register or Multiple Registers
Registers are used for position control and also for digital control and
can be accessed singly, or in multiples, with these codes. Function
code 06 writes a single 16 bit register while function code 16 can write
several in one transaction.
Code 07 - Read Exception Status
This is a specific short message function code which returns
predetermined discrete data from the MFU. The message is used to
allow fast transfer of a small data packet of 8 bits. A description of the
data is given in section 7.6.7.
Code 08 - Loopback Diagnostic Test
The purpose of the Loopback Test is to test the communication
system between the Modbus Module and the host. This code can be
regularly sent and used as a heartbeat to test the communications
link. The MFU supports this test when used with diagnostic code 00,
Return Query Data, and 02, Return Diagnostic Register. No other
diagnostic test codes are supported. See section 7.6.8.
Code 17 - Report Slave ID
This function code generates a response that contains the software
version of the MFU and actuator tag data. The tag data may be written
by the customer over the network. 12 ASCII characters can be written
in this area. See section 7.6.9.
Exception Response Codes
Error code 01 will be presented back to the host if the function code in
the data message is not one of those supported by the Modbus
Module or the message length is not as expected.
Error code 02 will be presented back to the host if the Data Address is
not valid for the Modbus Module.
Error code 03 will be presented back to the host if the value to be
written in a coil or register write is not valid for the register or coil
location chosen in the MFU.
Error code 06 will be presented back to the host if the MFU is unable
to respond with a correct message because it is busy.
