Samwontech TEMI 2500 - 6 MODBUS Protocol; MODBUS Frame Structure and Function Codes

SAMWONTECH
1st Edition of TEMI2000_Series IM : Dec. 15. 2008 Page 18 / 58
6. MODBUS Protocol
6.1 The Frame Structure of MODBUS protocol
▣ Data Format
Item ASCII RTU
Protocol Header :(Colon) N/A
Protocol Tail [CR][LF] N/A
Data length 7-bit(Fixed) 8-bit(Fixed)
Data type ASCII Binary
Error detecting
LRC
(Longitudinal Redundancy Check)
CRC-16
(Cyclic Redundancy Check)
Data time interval Under 1sec. Under 24-bit time
▣
The Frame Structure of MODBUS protocol
▶ Modbus ASCII
Protocol Header Address Function Code Data LRC Check Protocol Tail
1 character 2 character 2 character N character 2 character
2 character
(CR+LF)
▶ Modbus RTU
Protocol Header Address Function Code Data LRC Check Protocol Tail
N/A 8-Bit 8-Bit N * 8-Bit 16-Bit N/A
▪ N : Number of Hexadecimal data