Schweitzer Engineering Laboratories SEL-787 - Table E.27 61 H Read Parameter Enumeration Text Query Error Messages; Table E.28 7 Dh Encapsulated Packet with Control Command; Table E.29 7 Dh Encapsulated Packet Query Errors

E.16
SEL-787 Relay Instruction Manual Date Code 20081022
Modbus RTU Communications
Communications Protocol
The relay responses to errors in the query are shown below.
7Dh Encapsulated
Packet With Control
Command
The SEL-787 uses this function to allow a Modbus master to perform control
operations and another Modbus function with one query. The Device Net card
will transmit this command periodically to achieve high-speed I/O processing
and establish a heartbeat between the DeviceNet card and the main board.
Table E.29 shows the format of the relay responses to errors in the query.
Table E.27 61h Read Parameter Enumeration Text Query Error Messages
Error Error Code Returned
Communication
Counter Increments
Illegal parameter to read Illegal Address (02h) Invalid Address
Illegal enumeration in index Illegal Data Value (03h) Illegal Register
Table E.28 7Dh Encapsulated Packet With Control Command
Bytes Field
Queries from the master must have the following format:
1 byte Slave Address
1 byte Function Code (7Dh)
2 bytes Control Command (same as write to 2000h)
1 byte Embedded 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 Status Information (Register 2100h or 2101h
based on Bit 3 in Control Command Word)
1 byte Embedded Modbus Function
n bytes Optional data to support the Modbus function (0–250)
2 bytes CRC-16
Table E.29 7Dh Encapsulated Packet Query Errors
Bytes Field
Queries from the master must have the following format:
1 byte Slave Address
1 byte Function Code (7Dh)
2 bytes Status Information (Register 2100h or 2101h based on Bit 3 in
Control Command Word)
1 byte Modbus Function with Error Flag
1 bytes Function Error Code
a
a
If the embedded function code is invalid, then an illegal function code is returned here
and the illegal function counter is incremented. This error code is returned by the
embedded function for all valid embedded functions.
2 bytes CRC-16