IDEC FC6A-C16K1CE Communications Manual page 83

BCC Calculation Start Position
The start position for the BCC calculation can be specified from the first byte through the 15th byte. The BCC is calculated for the
range starting at the designated position up to the byte immediately before the BCC of the transmit data.
Example: Transmit data consists of 17 bytes plus 2 BCC digits.
(1) Calculation start position = 1
1st 2nd 3rd
STX "A" "B"
(2) Calculation start position = 2
1st 2nd 3rd
STX "A" "B"
BCC Calculation Formula
BCC calculation formula can be selected from XOR (exclusive OR), ADD (addition), ADD-2comp, Modbus ASCII, or Modbus RTU.
Example: Conversion results of transmit data consist of 41h, 42h, 43h, and 44h.
ASCII Data
"A" "B"
(41h) (42h)
(1) BCC calculation formula = XOR
Calculation result = 41h ⊕ 42h ⊕ 43h ⊕ 44h = 04h
(2) BCC calculation formula = ADD
Calculation result = 41h + 42h + 43h + 44h = 10Ah → 0Ah (Only the last 1 or 2 digits are used as BCC.)
(3) BCC calculation formula = ADD-2comp
Calculation result = FEh, F6h (2 digits without conversion)
(4) BCC calculation formula = Modbus ASCII
Calculation result = 88 (ASCII)
(5) BCC calculation formula = Modbus RTU
Calculation result = 85h 0Fh (binary)
FC6A S
4th 5th 6th
"C" "D" "E"
BCC calculation range
4th 5th 6th
"C" "D" "E"
BCC calculation range
"C" "D"
(43h) (44h)
M S A -
ERIES ICRO MART LL IN
5: U
15th 16th 17th 18th
"0" CR LF
15th 16th 17th 18th
"0" CR LF
-O T C M
NE YPE OMMUNICATION
C
SER OMMUNICATION
19th
BCC BCC
BCC
(2 digits)
19th
BCC BCC
BCC
(2 digits)
FC9Y-B1730
ANUAL
I
NSTRUCTIONS
5-7