Rockwell Automation Publication 2080-UM002L-EN-E - November 2021 215
Appendix B Modbus Mapping for Micro800
7. From the Parameter window, change the following Parameters to set the
communications for Modbus RTU so that the PowerFlex 4M Drive
communicates with Micro830/850/870 via Modbus RTU communication.
8. Disconnect the Communications and save your project.
9. Turn off the power to the drive until the PowerFlex 4M display blanks out
completely, then restore power to the PowerFlex 4M.
The drive is now ready to be controlled by Modbus RTU communication
commands initiated from the Micro830/850/870 controller.
Modbus devices can be 0-based (registers are numbered starting at 0), or 1-
based (registers are numbered starting at 1). When PowerFlex 4-Class drives
are used with Micro800 family controllers, the register addresses listed in the
PowerFlex user manuals need to be offset by n+1.
For example, the Logic Command word is located at address 8192, but your
Micro800 program needs to use 8193 (8192+1) to access it.
EXAMPLE: Modbus Address (n+1 value shown)
8193 Logic Command word (Stop, Start, Jog, and so on)
8194 Speed Reference word
xxx.x format for 4/4M/40, where "123" = 12.3 Hz
xxx.xx format for 40P/400/400N/400P, where "123" = 1.23 Hz
8449 Logic Status word (Read, Active, Fault, and so on.)
8452 Speed Feedback word (uses same format as Speed Reference)
8450 Error Code word
(n+1) To access Parameter
See the respective PowerFlex 4-Class drive User Manual for additional
information about Modbus addressing. See Appendix E – Modbus RTU
Protocol, on publication 22C-UM001
.
Table 45 - Modbus RTU Parameters
Parameter Description Setting
C302 Comm. Data Rate (Baud Rate) 4 = 19200 bps 4
C303 Communication Node Address (address range is 1…127) 2
C304
Comm. Loss Action (Action taken when loss communication) 0 = Fault with coast
stop
0
C305
Comm. Loss Time (Time remain in communication before taking action set in
C304) 5 sec (Max. 60)
5
C306 Comm. Format (Data/Parity/Stop) RTU:8 Data Bit, Parity None, 1 Stop bit 0
If the respective PowerFlex drive supports Modbus Function Code 16 Preset
(Write) Multiple Registers, use a single write message with a length of "2" to
write the Logic Command (8193) and Speed reference (8194) at the same
time.
Use a single Function Code 03 Read Holding Registers with a length of "4" to
read the Logic status (8449), Error Code (8450), and Speed Feedback (8452)
at the same time.
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