Electro-Sensors HazardPRO Series, Руководство по установке

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MODBus Read Command Example
Request Response
Field Name (Hex) Field Name (Hex)
Function 0x03 Function 0x03
Starting Address High 0x01 Byte Count 0x06
Starting Address Low 0x91 Register Value High (401) Value
No. of Registers High 0x00 Register Value Low (401) Value
No. of Registers Low 0x03 Register Value High (402) Value
Register Value Low (402) Value
Register Value High (403) Value
Register Value Low (403) Value
*All Values are base 10 unless expressed in hex notation (0X00)
Most PLC’s have simple ladder instructions that read and write Modbus values. The following
information details the data packet layout of the Modbus transactions. In most cases, it will not
be necessary to understand the content of the transaction to utilize the PLC instructions
Example Read
Example request to read registers 401 to 403
Byte Description Default Value Remarks
0 Transaction Identifier High Byte Number to track request. Response will
include this number.
1 Transaction Identifier Low Byte
2 Protocol Identifier High Byte 0 All Modbus commands must be
protocol 0.
3 Protocol Identifier Low Byte 0
4 Length High Byte 0 Start counting at byte 6. Length will
always be 0x06 for this command.
5 Length Low Byte 0x06
6 Device ID ID of device being requested.
7 Function 0x03 Modbus function identifier.
8 Read Address Start High Byte NOTE: Unless your software is using
zero based addressing this will typically
be one less than the starting address
you request in the TCP IP packet.
9 Read Address Start Low Byte
10 Read Length High Byte
11 Read Length Low Byte
*All Values are base 10 unless expressed in hex notation (0X00)
TCP IP Data Packet Detail
Request Structure