Chapter 5: DURAPULSE MODBUS Communications
5–38
Dir ectLOGIC Modbus Ladder Programming
The set up for all of the DirectLogic CPUs is very similar. However, there may be
some subtle differences between CPUs. Refer to the appropriate CPU User
Manual for the specifics on your DirectLogic CPU.
The following ladder program shows some examples of how to control the
DURA
PULSE AC drive through Modbus RTU. The drive should be setup and tested
for communications before it is connected to a load.
Separate Run Command Write Instruction
Why do we write the Run Command with a separate write instruction? If we
write the Run Command to the drive along with the Speed Reference, Direction,
External Fault, and Fault Reset Commands, we can keep the parameter addresses
in sequence, and we can update all five of the commands with one write
instruction. This method is valid only if we disable the drive’s keypad STOP
button (P3.00 = 04).
Typically, the keypad STOP button will be enabled (P3.00 = 03), and we need to
prevent a change in one of the other commands from overriding a keypad Stop
Command by causing a previous Run Command to be rewritten to the drive. By
using a separate Run Command write instruction, only a deliberate Run
Command change by the program will run the drive again after a stop.
Block Transfer Parameters for Modbus Programs
For writing to any of the parameters from P0.00 to P8.02, a group of 15 block
transfer parameters (P9.11 to P9.25) is available in the DURA
PULSE AC drive. This
sequential block of parameters can be used to "group" various miscellaneous non-
sequential parameters, so that you can update the parameters in one programming
write block instead of having to use multiple write commands.
For example, it would typically take three different write commands to change the
three non-sequential parameters Accel Time 1 (P1.01), Accel S-curve (P1.03), and
Multi-speed 1 (P5.01).
However, you could make the same three changes using one write command by
setting P9.11 to P1.01, P9.12 to P1.03, and P9.13 to P5.01, so that the parameters
become sequential.
These programs are for illustrational purposes only,
and are not intended for a true application.
WARNING: Write programs in such a way that the program does not erroneously
overwrite a remote Stop command with a Run command, such as when P3.00 is set
to 03. This example program prevents such an accidental overwrite.
WARNING: A drive should never be connected to a load until any applicable
communication programs have been proven.
DURAPULSE AC Drive User Manual
1st Ed. Rev. D 05/2013
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