Submittal Sheet

7800 SERIES S7800A2142 KEYBOARD DISPLAY MODULE
32-00110—05 54
APPENDIX E: MODBUS FUNCTION
See “Appendix A: Display Setup” on page 28 for Setup.
OPERATION
The S7800 ModBus
TM
Data Feature enables terminal 1, 2 to Data + and Data -. Table 16 provides register mapping. It
identifies the mapping of the 7800 SERIES parameters to ModBus
TM
registers.
Function Codes
Supported function codes of Modbus Protocol Reference Guide (PI-MBUS-300 Rev. J) are 3, 4, 6, 16, and 17. Function
codes 3 and 4 are treated the same by the S7800. Two registers should be read when the data format is a U32 value (4
bytes); if both registers are not read, then data for a part of the value is returned. U32 values are either in Big-endian or
Little-endian format. The maximum number of addresses that can be queried is 127 (0x7F) for each query message.
Table 9 through 12 provide information on the function codes.
NOTE: All Query and Response cells below are 1 byte.
Table 9. Query Message Format for Function Codes 3 and 4.
Table 10. Response Message Format for Function Codes 3 and 4.
Table 11. Query Message Format for Function Code 6 .
Table 12. Response Message Format for Function Code 6 (There is no response if the query was broadcast.)
Table 13. Query Message Format for Function Code 17.
NOTE: See Table 17 for function code 17 response format.
Table 14. Exception Response Message Format.
Slave
Address
Function
Code
Starting
Address High
Starting
Address Low
Number of
Addresses High
Number of
Addresses Low CRC CRC
01 03 or 04 00 0A 00 01 A4 08
Slave Address Function Code Byte Count Data High Data Low CRC CRC
01 03 or 04 02 00 22 38 5D
Slave
Address
Function
Code
Starting
Address
High
Starting
Address Low
Preset Data
High
Preset Data
Low CRC CRC
01 06 00 7F 00 04 B9 D1
Slave
Address
Function
Code
Starting
Address
High
Starting
Address Low
Preset Data
High
Preset Data
Low CRC CRC
01 06 00 7F 00 04 B9 D1
Slave
Address
Function
Code CRC CRC
03 11 C1 4C
Slave
Address
Function
Code
+ 80h
Exception
Code
CRC CRC