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V: 1.0 Revised: Jan. 2018
AcuRev 1310
68
DIN-Rail Power Meter
Function Field
When a query is sent from the master to a slave device, the function code filed tells the slave
what kind of action to perform.
Table 5-2 Function Code
Function Code
Meaning
Action
03
Read Holding Register
Obtain current value of 1 or more registers
16
Preset register
Set value of 1 or more register
01
Reading Relay RO Status
Get the current state of the relay of the RO
Output (ON/OFF)
05
Control relay RO state
Control relay RO Output state (ON/OFF)
Data Field
The data field contains the data that the slave device needs in order to complete the request.
This data may be a numerical value, address or settings. For example, the function code tells
the slave device to read one register, however the data field specifies readings from which regis-
ter and how many registers to read.
Error Check Field
This field allows for error checks to be performed by both master and slave devices. Sources of
errors such as electrical noise and other interferences can cause the data to be changed while
it is being transmitted from one device to another. The error check ensures that the master or
slave devices do not respond to the distorted data during the transmission. The error check rule
used is the bit Cyclic Redundancy Check (CRC16).
5.2 Communication Format
Table 5-3 Protocol Illustration
Addr
Fun
Data start
register hi
Data start
register lo
# of regis-
ters hi
# of regis-
ters lo
CRC16 Hi
CRC16 Lo
06H
03H
00H
00H
00H
21H
84H
65H
Addr: Slave device address
Fun: Function code
Data start register hi: High byte of starting register address
Data start register lo: Low byte of starting registers address
