CHAPTER 7: MODBUS COMMUNICATIONS MODBUS FUNCTIONS
PQM POWER QUALITY METER – INSTRUCTION MANUAL 7–13
7.2.9 Function Code
16 -
Performing
Commands
Some PLCs may not support execution of commands using function code 5 but do support
storing multiple setpoints using function code 16. To perform this operation using function
code 16 (10H), a certain sequence of commands must be written at the same time to the
PQM. The sequence consists of: Command Function register, Command operation register
and Command Data (if required). The Command Function register must be written with the
value of 5 indicating an execute operation is requested. The Command Operation register
must then be written with a valid command operation number from the list of commands
shown in the memory map. The Command Data registers must be written with valid data if
the command operation requires data. The selected command will be executed
immediately upon receipt of a valid transmission.
MESSAGE FORMAT AND EXAMPLE:
Perform a reset on PQM (operation code 1).
Table 7–8: Master/Slave Packet Format for Performing Commands
MASTER
TRANSMISSION
BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 10 store multiple setpoints
DATA STARTING
ADDRESS
2 00 80 setpoint address 1028
NUMBER OF
SETPOINTS
2 00 02 2 setpoints = 4 bytes total
BYTE COUNT 1 04 4 bytes of data
DATA 1 2 00 05 data for address 0080
DATA 2 2 00 01 data for address 0081
CRC 2 B0 D6 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave 17
FUNCTION CODE 1 10 store multiple setpoints
DATA STARTING
ADDRESS
2 00 80 setpoint address 00 80
NUMBER OF
SETPOINTS
2 00 02 2 setpoints
CRC 2 46 7A CRC error code
Courtesy of NationalSwitchgear.com
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