Error Check; Crc-16 Calculation Example; Header, Trailer (Silent Interval) - Omron JX User Manual

4-2 Function Mode
Function code
Function code
01h Coil status reading
03h Holding register content reading
05h Writing into the coil
06h Writing into holding register
08h Loopback test
0Fh Writing into multiple coils
4
10h Writing into multiple registers
<Error Check>
•CRC (Cyclic Redundancy Check) is used for the ModBus-RTU error check.
•The CRC code is 16-bit data generated for the block of random length data in the 8-bit unit.
•To generate the CRC code, the generation polynomial CRC-16 (X

CRC-16 Calculation Example

<Header, Trailer (Silent interval)>
•Wait time between receiving the query from the master and the response by the Inverter.
•Be sure to provide the 3.5-character length for wait time. If the length does not reach 3.5
characters, the Inverter does not respond.
•The actual communication wait time is the total of the silent interval (3.5-character length) and
C078 (communication wait time) setting.
4-68
Maximum number of data
Function
CRC-16
calculation
*1
CRC =FFFFh
Exists
Target data
All target data
completed
Interchange Hi and Lo
*1
bytes of CRC
Completed
Maximum data number in 1
bytes in 1 message
4 32 coils (in bits)
8 4 registers (in bytes)
2 1 coil (in bits)
2 1 registers (in bytes)
⎯
4 32 coils (in bits)
8 4 registers (in bytes)
16
+X
*1
CRC
Hi Lo
CRC register (2 bytes)
*1 *1
CRC = CRC XOR target data
Completed
8-bit shift
Bits left
*1 *1
CRC = Shift CRC by 1 bit
to the right
0
Overflow bit
after shift
1
*1 *1
CRC =CRC XOR A001h
Shift by 1 byte against target data
message
⎯
15 2
+X +1) is used.