Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 947

Processing details
• These instructions generate the CRC value for (n) 8-bit data (unit: byte) starting from the device specified by (s), and store
the CRC value to the device specified by (d). "X
(CRC-16). The 16-bit conversion mode and 8-bit conversion mode are available for these instructions. The conversion
mode can be selected by turning on or off SM772.
• If the value specified in (n) is 0, no processing is performed.
• These instructions calculate the CRC (cyclic redundancy check) value which is an error check method used in
communication. In addition to CRC, there are other methods to check an error, such as parity check and sum check
(checksum). For obtaining the horizontal parity value and sum check value, the CCD(P) instruction is available. ( Page
903 CCD(P))
• The operation in each conversion mode is described below.
■16-bit conversion mode (while SM772 is OFF)
In this mode, the CRC operation is executed for upper 8 bits (in units of byte) and lower 8 bits (in units of byte) of the device
specified by (s). The operation result is stored to 16 bits in one device specified in (d).
Ex.
When (n)=6
In 16-bit conversion mode, the six bytes in the following shaded portion become an operation target. The CRC value is
determined as "A57BH", and therefore "A57BH" is stored in the device specified by (d).
Decimal Hexadecimal
Upper
D0 24932 61H 61H 61H
D1 4219 10H 10H 10H
D2 -1333 FAH FAH FAH
D3 -1 FFH
D4 32761 7FH
D5 10000 27H
■8-bit conversion mode (while SM772 is ON)
CRC operation is executed only for lower 8 bits (lower byte) of the device specified by (s). With regard to the operation result,
lower 8 bits (in units of byte) are stored to the device specified by (d), and upper 8 bits (in units of byte) are stored to a device
specified by (d)+1.
Ex.
When (n)=6
In 8-bit conversion mode, the six bytes in the following shaded portion become an operation target. The CRC value is
"BDA1H" and therefore "A1H" is stored in the device specified by (d) and "BDH" is stored in the device specified by (d)+1.
Decimal Hexadecimal
Upper
D0 24932 61H
D1 4219 10H
D2 -1333 FAH
D3 -1 FFH
D4 32761 7FH
D5 10000 27H
Operation error
Error code Description
(SD0)
3405H A digit other than 4 is specified in the digit-specified bit device in (s) and (d).
16 15 2
+ X + X
Lower
64H 64H 64H
7BH 7BH 7BH
CBH CBH CBH
FFH
F9H
10H
Lower
64H 64H 64H
7BH 7BH 7BH
CBH CBH CBH
FFH FFH FFH
F9H F9H F9H
10H 10H 10H
+1" is used in the generator polynomial of the CRC value
7 APPLICATION INSTRUCTIONS
7.20 Data Processing Instructions
7
945