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xcyong89 · Junior Joined: 22 Sep 2018 Posts: 14

Hi,

I have setup the Simple PLC communication in RJ71C24 (Channel 2) for communication between Mitsubishi IQ-R series PLC (Mosbus RTU Master) and multi drop Modbus RS485 Slave devices. The Simple PLC Communication Setting shows below:

GX Works3 Simple PLC Communication Error Indicator GX Works3 Simple PLC Communication Error Indicator

GX Works3 Simple PLC Communication Error Indicator GX Works3 Simple PLC Communication Error Indicator

Just wonder is there any communication error flag to indicate communication fail for each communication request in Simple PLC communication ?

Antterra · Junior Joined: 27 Sep 2022 Posts: 4

Calculation procedure for 16-bit CRC (for MODBUS)
This is an error check method to be used when data are transmitted/received with the RTU mode of the MODBUS protocol.
The data length of CRC is fixed to 2 bytes (16 bits), and the CRC is calculated every 1 byte (8 bits) from the start of the
calculating range according to the following procedure.
1. Load a 16-bit register whose bits are all '1'.
2. Exclusive OR (XOR) the first 1 byte (8 bits) of the calculating range with 8 bits in above 1.
3. Shift the result of the step 2. for one bit right.
4. If the least significant bit in above 2. is '1', exclusive OR (XOR) the result of 3. with the generator polynomial (A001H). If
the least significant bit is '0', shift the result of step 3. one bit right (operation described in 3.) without the exclusive OR
(XOR) operation.
5. Repeat steps 3. and 4. for 8 times.
6. Exclusive OR (XOR) the result of the above 5 with the next 1 byte (8 bits).
7. Repeat step 3 through 6 until all bytes have been processed. The final result is CRC value.
8. The CRC value is stored in a packet in the order of lower 8 bits  upper 8 bits.
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