Download Operating Instructions - Cont

"Easy" Startup with RS-485 Interface/Fieldbus
Function with RS-485 master
I
7
0
7.4.7
Block check character BCC
The block check character (BCC) is used in conjunction with even parity formation to ensure reliable data transfer. The block check character is formed by means of an XOR
logic operation of all message characters. The result is entered in the BCC at the end of
the message.
Example
The following figure gives an example of how a block check character is created for an
acyclical message of type PDU 85hex with 3 process data items. The XOR logic operation on the characters SD1...PO3low results in the value 13hex as the block check character BCC. This BCC will be sent as the last character of the message. The recipient
checks the character parity after having received the individual characters. Following
this, the block check character is created from the received characters SD1...PO3low in
accordance with the procedure below. The message has been correctly transmitted if
the calculated and received BCCs are identical and there is no character parity error.
Any other result will be displayed as a transmission error. The message may have to be
repeated.
PO
01 hex
85 hex
00 hex
06 hex
20 hex
00 hex
ADR
TYP
PO1high
PO1low
PO2high
PO2low
Stop
SD1
SD1
0B hex
B8 hex
13 hex
PO3high
PO3low
BCC
Start
02 hex
Parity
Idle
: 02 hex
1
0
0
0
0
0
0
1
0
ADR : 01 hex
1
0
0
0
0
0
0
0
1
TYP
: 85hex
1
1
0
0
0
1
0
0
1
PO1high : 00 hex
0
0
0
0
0
0
0
0
0
PO1low : 06 hex
0
0
0
0
0
1
0
1
0
PO2high : 20 hex
1
0
0
1
0
0
0
0
0
PO2low : 00 hex
0
0
0
0
0
0
0
0
0
PO3high : 0B hex
1
0
0
0
0
0
1
1
1
PO3low : B8 hex
0
1
0
1
1
0
1
0
0
BCC : 13hex
1
0
0
0
1
0
0
1
1
XOR
XOR
XOR
XOR
XOR
XOR
XOR
XOR
640978571
Operating Instructions – MOVIMOT® MM..D With AC Motor DRS/DRE/DRP
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