16
7.1 MODBUS-RTU protocol
VII. Communication Protocol Description
7.2 Communication frame format description
The following chart shows the meaning of exception error codes:
7.1.5 Communication frame delay
7.1.2 Data Format
Data Bit
Checking Bit
Stop Bit
1
8
None, Even, Odd checking(Programmable)
1
Start Bit
Hosting Sending
Slave address
Function Code
Start Add
Data Length
CRC Code
Bytes
1
1
2
2
2
Information Send
01
03
0x4000
0x0002
0xD1CB
Remark
Send to slave at address 01
Read register
Start Add
Read 2 registers (4 bytes in total)
The host calculates the CRC code
Error code Name
Description
0X01
0X02
0X03
0X04
Function code error
Variable address error
The limit of the data value
Incorrect or out of frame length
The meter received an unsupported function number
The data value sent by the host exceeds the data range corresponding to the instrument or the data
structure is incomplete
The function code and the communication frame length are inconsistent or request exceeds the limit
The host specified data location is over the range of the meter or an illegal register operation has been
received
7.1.1 MODBUS-RTU communication protocol,adopts RS485 half-duplex communication to check 16-bit CRC.The meter does not return
the check error.
1. All RS485 loop communication should follow master and slave mode.In this way, information and data are transferred between a single
master station and up to 32
2. The master station will initialize and control all the information transmitted on the RS485 communication loop ( daisy chain );
3. In any case, communication cannot be started from a slave station
4. Communication on all RS485 loops takes place in a "packaged" manner. A data packet is a communication frame.A packet can
contain up to 128 bytes.
5. The master station sends called request and the slave sends called response.
；
6. In any case, the slave can only respond to one request from the master station;
7.1.4 Communication exception handling
If the master sends an illegal packet or if the master requests an invalid data register, an abnormal data response will be generated. This
abnormal data response consists of the slave address, function code, fault code, and check field. When the high-order bit position of the
function code domain is 1, it indicates that the data frame at this time is an abnormal response.
According to MODBUS communication requirements, abnormal response function code = request function code + 0x80; when abnormal
response occurs, the highest position of function number is 1. For example, if the host request function number is 0x04, the function
number returned from the slave corresponds to 0x84.
7.2.1 Function Code“03”:Read multiple register input
Eg:The host reads the UA (A phase voltage), and it is measured that the A phase voltage is 220.0V. The UA's address code is 0x4000
because UA is a fixed-point number (4 bytes) and occupies 2 data registers. The corresponding hexadecimal data of 220.0V is:
0x0000898 (200)
Host sent message format: (default high word first)
There should be an appropriate delay between the requests from the master station for the two frames. When the baud rate is 9600.
In order to ensure a correct response, it is recommended that a 300mS delay be reserved between the two frames. When the baud rate
decreases, the communication delay should increase appropriately.
7.1.3 Communication frame format
Frame Content
Bytes
Instructions
Slave Station Add
1
1
2
Valid slave address range is 1-247
The length of data that needs to be read or written
The location where the data area is stored when the slave executes a valid command. Different variables occupy
different number of registers, some address variables occupy two registers, 4 bytes of data, some variables occupy
a register,2 bytes of data, please use according to the actual situation
Function Code
Data Add
2
Data length
Slave station returns data or master data to be written
Variable
Data
The MODBUS-RTU mode uses 16-bit CRC. The sending device shall calculate CRC16 on each data in the parcel, and the
final result shall be stored in the test domain. The receiving device shall also calculate CRC16 on each data (other than
the check field) in the parcel and compare the result field check fields. Only the same package can be accepted.
2
CRC Check Code
Read one or more current register values
Writes the specified value to an internal register
0X03
0X06
0X10
Writes the specified value to multiple internal registers
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VI.EVENT RECORD DESCRIPTION
Event recording is currently an optional feature and can only be read through communications. The specific instructions are
as follows:
Eg, To read the latest first record,
the data is as follows
：
“01 03 45 00 00 07 13 EC”
Answers are as follows
：
“01 03 0E 00 01 00 0E 00 09 00 12 00 11 00 07 00 21 0C F7”
Indicates that the event is a modified parameter. The moment of occurrence is
014-9-18 17:07:33
6.3 Reading of event records
ADD
XX
Order
03
Data ADD
45
XX
Data length
00
07
CRC
XX
XX
No.
Correspondence data
1
1
Power on the meter
Event Desciption
2
2
modified parameter
3
3
Clear Energy
4
4
Clear Demand
5
5
Clear Event
6
6
Clear maximum
7
7
1st alarm action
8
8
1st alarm end
9
9
2nd alarm action
10
10
2nd alarm end
V. SIMPLE TROUBLESHOOTING
Power failed to join the device
Incorrect voltage measurement
Incorrect current measurement
Incorrect power measurement
Switching voltage
No control command received
Incorrect relay operation mode
The measurement value
is incorrect or does not
meet expectations
Switch status does
not change
Relay does not operate
The upper end cannot
communicate with the
device
Device communication address is incorrect
Device communication rate is incorrect
Communication link is not connected to
terminating resistor
Communication link is disturbed
Communication line interruption
Check whether the correct operating voltage is added to the L/+ and N/- terminals of the device
Check if control power fuse is burned
Check if the neutral connection is reliable
Check whether the measured voltage matches the rated parameter of the equipment
Check if the PT ratio parameter setting is correct
Check whether the measured current matches the rated parameter of the device
Check CT ratio parameter setting is correct
Check the measurement mode setting is correct
Check the voltage and current phase sequence is correct
Check the current name is wrong
Check whether the external node type matches the device's rated parameters
Check the external wiring is correct
Check the communication link is correct
Check current relay is in correct mode
Check whether the device address is consistent with the definition
Check whether the device communication rate is consistent with the definition
Check whether the 120 ohm resistor is added
Check that the communication shield is well grounded
Check the communication cable is disconnected
Reason
Solution
Problem
No display after adding
control power
6.2 Event Record Format
Event Type
1-10
Year
Month
Day
Hour
Minute
Second
Event Occurred Time
A total of 32 groups of events were included, both of which included event types and times. The event record uses a
sequential recording method: the first record is always the most latest event and extends back to a total of 32 records.
6.1 Event Types
Including the followed 10 types
：
