-113-
When transparent mode
・
If you check “Transparent mode” at “BCC” in the
“
Configuration”, it calcuｌate “BCC” as transparent mode.
・
The character set to “DLE code” is treated as a Data Link Escape code (hereafter, DLE).
・
The received frame that starts with DLE + calculation start code has the calculation range up to DLE + cal-
culation end code, and the calculation end code without DLE is treated as a normal character.
・
DLE is excluded from BCC calculation. However, if two DLEs continue, the second DLE is treated as a nor-
mal character and is therefore subject to BCC calculation.
・
Synchronization code without DLE is treated as a normal character, and synchronization code with DLE is
excluded from the calculation.
9.1 Calculation of the Block Check
The block check is executed as follows.
ڦ
For ASYNC, SYNC, and BSC
Calculation
start
:
When it receives a calculation result by “ITB code ” or a character set at “Begin code” of
“BCC” in the
“
Configuration”, it starts calculation from the next character.
Calculation
end
:
When it receives either the “ITB code ” or the character set at “End code” of “BCC” in the
configuration it finishes the calculation including that character.
BCC judgment
: When the calculation end character is received after the calculation start character is re-
ceived, the next data of the calculation end character is checked as BCC.
Chapter 9 Documents
ڦ
For MODBUS
The calculation range is from the address field to data field.
ڦ
For HDLC and SDLC
・
Calculation start: After the flag synchronization is established, it starts the calculation from
the first received data.
・
Calculation end: It calculates up to the character immediately before the sync release flag.
・
FCS judgment: The character immediately before the sync release flag is checked as FCS.
SY SY DL SX A
B C DL SY DL SY D
E F DL G
H
EX I J K
DL EX 1E 94
Excluded from calculation Excluded from calculation Excluded from calculation BCC
Calculation range
Address
Function code
data
BCC/CRC
Calculation range
S
X
A
B
C
U
S
A0
D
E
F
G
E
X
FC
BCC code
BCC code
S
X
A
B
C
D
E
F
G
E
X
BC
BCC code
Calculation start character
Calculation end character
Calculation range
Calculation range
Calculation end character
Calculation range
Calculation start character
ITB code
