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
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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
