ICP DAS USA M-7065 User Manual page 15

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.
LRC Calculation:
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.
Example :
Modbus RTU => 01 46 00 [ 12 60 ]
Modbus ASCII => :014600B9(CR•LF)
(1.) hexadecimal = 01h+46h+00h = 47h
(2.) 2's complement: = B9h (LRC)
Technical Support
If you have problems about using the M-7065 DIO module,
please contact ICP DAS Product Support.
Email: Service@icpdas.com
M-7065 User's Manual Ver2.0, Dec. /200 8 ---15