Input and Output Signals
Publication PUB091-003-00_0119
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5.1.2
Modbus Control using Individual Coil commands
The open, close, stop, ESD and DO-1 to DO-4 controls can be written using function code 05 or 15 to
write to single or multiple coils. Writing the value FF00 turns a coil on and 0000 turns it off. The MFU
provides a degree of intelligence in operating the coils for the open, close, stop and ESD functions.
When one coil is turned on, all the others are turned off, so only one can be on at a time. The actuator
will obey the last command it receives, so if two writes using function code 05 follow each other closely
the last one will win.
A multiple coil write by function code 15 to turn on more than one of the open, close, stop and ESD
coils in the same command is not permitted. If an attempt to energise more than one of these coils in
one command is made an exception response is generated and the multiple write ignored.
With the open and close coils these will turn off once the actuator completes the command, a new
command is sent, the actuator is placed in local or some other interruption occurs. For example the
close coil will de-energise once the actuator reaches the close position and stops. The stop and ESD
coils remains latched once turned on and are cleared by another command or writing 0 to the coil.
The ESD action works slightly differently in that even if the coil is reset to 0, the action remains latched
in the actuator. This is because a network ESD command overrides the actuator local controls. In
order to remove the ESD action it is necessary to write a new command and if the actuator has local
selected then the only command that will clear the latch is a write to the stop coil.
In the case of the DO-1 to DO-4 relays they will follow the command, energising when turned on and
de-energising when turned off. These relays also maintain their status if the actuator power is
removed and reset to the de-energised state only when the power is restored.
5.1.3
Modbus Control using the ACTCON Register
A single register is provided to allow the digital control of the actuator. Writing a value to the register
with function code 06 or 16 causes the actuator to open, close, stop or ESD and at the same time
cancels any other command set. This method of control removes the need to reset commands written
with a code 05 coil write with a second write to the same location. The number written changes any
coil states already set to the new value.
ACTCON Register (Register 5)
Value
Stop
Close
Open
ESD
0
1
2
3
4 – 255
No action
No action
No action
No action
5.1.4
Modbus Control using the Actuator Position DV register
The analogue position control function will take priority over an earlier coil or ACTCON register
command to open, stop, close or ESD the actuator when a value is written to the Actuator Position DV
register. The controller will then position the actuator to the desired value.
The analogue position control function is cancelled either by the actuator achieving the desired
position or a coil or ACTCON register write to one of the open, stop, close, ESD coils.
