Despatch Protocol Plus Modbus Communications - Manual (Page 46)

Chromalox Instruments and Controls
A-51643 Rev. 6 10/06/03 40
Figure 6 CRC Flowchart
6.7 Field Contents in Modbus Messages
The following tables show examples of a Modbus query and a normal response in RTU mode.
Start
CRC
16
= $FFFF
CRC
LO
= CRC
LO
Data
N=0
Grab first byte of message
Logical Shift Right CRC
16
(0 CRC
16
C)
Test C CRC
16
= CRC
16
$A001
N = N+1
N = 8?
Get next message byte
Last message
byte?
Stop
1
0
No
Yes
No
Yes