IDEC MicroSmart - Manual (Page 300)

17: U SER C OMMUNICATION I NSTRUCTIONS
17-22 « FC4A M ICRO S MART U SER ’ S M ANUAL »
Conversion Type
The BCC calculation result can be converted or not according to the designated conversion type as described below:
Example: BCC calculation result is 0041h.
(1) Binary to ASCII conversion
(2) No conversion
BCC Digits (Bytes)
The quantity of digits (bytes) of the BCC code can be selected from 1 or 2.
Example:
Comparing BCC Codes
The MicroSmart compares the BCC calculation result with the BCC code in the received incoming data to check for any
error in the incoming communication due to external noises or other causes. If a disparity is found in the comparison, an
error code is stored in the data register designated as receive status in the RXD instruction. For user communication error
code, see page 17-27.
Example 1: BCC is calculated for the first byte through the sixth byte using the XOR format, converted in binary to
ASCII, and compared with the BCC code appended to the seventh and eighth bytes of the incoming data.
0041h
Binar y to ASCII conversion
“4”
(34h)
“1”
(31h)
2 digits
Note: On WindLDR, Modbus ASCII is
defaulted to binar y to ASCII conversion.
0041h
No conversion
NUL
(00h)
“A”
(41h)
2 digits
Note: On WindLDR, Modbus RTU is
defaulted to no conversion.
(1) BCC digits = 2
“4”
(34h)
“1”
(31h)
“4”
(34h)
“1”
(31h)
(2) BCC digits = 1
“4”
(34h)
“1”
(31h)
“1”
(31h)
Lower digit
Note: On WindLDR, Modbus ASCII and
Modbus RTU are defaulted to 2 digits.
“1”
(31h)
“2”
(32h)
BCC Calculation Range
“3”
(33h)
“4”
(34h)
Incoming Data
“5”
(35h)
“6”
(36h)
“0”
(30h)
“7”
(37h)
BCC
31h
⊕ 32h ⊕ 33h ⊕ 34h ⊕ 35h ⊕ 36h = 07h
“0”
(30h)
“7”
(37h)
BCC Calculation Result
Binar y to ASCII Conversion
Comparison result is true to indicate
that data is received correctly.