EUCHNER HBAS - Manual (Page 7)

EUCHNER Hand-Held Pendant Station
3.3 BCC Block Check Character
The
BCC (Block Check Character) is defined by calculation.
During this process an EXCLUSIVE-OR operator is applied to all characters after STX.
The result is added at the end as the BCC character.
XOR operator
STX Data block DLE ETX BCC
Calculation:
1st character in the data block
XOR 2nd character in the data block
XOR nth character in the data block
XOR last character in the data block
XOR DLE
XOR ETX
= BCC
Simplification:
As the 2 special characters
ETX and DLE are always present, these can be combined and
calculated separately to the actual data block.
03H XOR 10H = 13H
The result for the data block is the subjected to an
EXCLUSIVE-OR operation with the constant 13H.
BCC = (XOR data block) XOR 13H.
3.4 Examples for the determination of the BCC
Example 1: The HBAS sends the key 7 (37H):
Byte 1 STX
Byte 2 37H (37H)
Byte 3 DLE (10H)
Byte 4 ETX (03H) XOR operator
Byte 5 BCC
37H XOR 10H = 27H
27H XOR 03H = 24H
Simplification by combining DLE and ETX :
37H XOR 13H = 24H
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