Modbus Ascii Protocol - ICP DAS USA M-7065 User Manual

4. Modbus ASCII Protocol

Using Modbus ASCII Protocol, all command are coded
in hexadecimal values, represented with readable ASCII
characters. Only the characters 0...9 and A...F are used
for coding.
Using Modbus ASCII Protocol, characters are used to
start and end a frame. The Leading Character ':' is used
to flag the start of a command and each command is
ended with a CR•LF combination. The LRC characters
are appended to the command preceding the CR•LF
characters.
Command Format:
Leading
Character Address
Response Format:
Leading
Character
Calculation:
LRC
All characters except for Leading Character (:) and delimiter
(CR•LF) are added with a carry being discarded.
Total value is converted to binary notation, is converted to 2's
complements, then to hexadecimal figures, that is, LRC.
M-7065 User's Manual Ver2.0, Dec. /200 8 ---141
Module
Command
Module
Data
Address
[LRC] CR LF
[LRC] CR LF