Siemens SIMATIC CP 340 - Block Checksum

Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03
33
2.4.2 Block Checksum
Block Checksum
With the 3964R transmission protocol, data integrity is increased by the additional sending of
a block check character (BCC).
%&&ඎ
;25  
;25   
   
;25   
   
;25   
   
   
   
+ඎ+ඎ+ඎ+ඎ+ඎ+ඎ+
67; %&&'/((7;'DWD
0HVVDJHIUDPH
Figure 2-5 Block Checksum
The block checksum is the even longitudinal parity (EXOR operation on all data bytes) of a
sent or received block. Its calculation begins with the first byte of user data (first byte of the
message frame) after the connection setup, and ends after the DLE ETX code on connection
release.
Note
If DLE duplication occurs, the DLE code is accounted for twice in the BCC calculation.