Rockwell Automation Publication 825-UM004D-EN-P - November 2012
143
Modbus RTU Communications
Chapter
10
7Dh Encapsulated Packet
With Control Command
The 825-P uses this function to allow a Modbus master to perform control
operations and another Modbus function with one query. This command will be
transmitted periodically to achieve high-speed I/O processing and also serve as a
heartbeat between the communication option card and the main board.
The format of the relay responses to errors in the query is shown in Table 82.
Table 82 - 7Dh Encapsulated Packet Query Errors
Bytes
Field
Requests from the master must have the following format:
1 byte
Slave Address
1 byte
Function Code (7Dh)
2 bytes
Subfunction (2000h)
1 byte
Modbus Function
n
bytes
Optional Data to Support Modbus Function (0…250)
2 bytes
CRC-16
A successful response from the slave will have the following format:
1 byte
Slave Address
1 byte
Function Code (7Dh)
2 bytes
Subfunction (2100h or 2101h)
1 byte
Function Code (7Eh)
n
bytes
Optional Data to Support Modbus Function (0…250)
2 bytes
CRC-16
Bytes
Field
Requests from the master must have the following format:
1 byte
Slave Address
1 byte
Function Code (7Dh)
2 bytes
Subfunction (2100h or 2101h)
1 byte
Function Code (7Eh)
1 byte
Function Error Code
2 bytes
CRC-16
Summary of Contents for 825-P
Page 1: ...Modular Protection System for Motors Catalog Number 825 P User Manual...
Page 4: ...4 Rockwell Automation Publication 825 UM004D EN P November...
Page 64: ...64 Rockwell Automation Publication825 UM004D EN P November 2012 Chapter 5 Using MPS Explorer...
Page 234: ...234 Rockwell Automation Publication 825 UM004D EN P April 2012 Chapter B ParameterList...
Page 265: ......