4-2 Function Mode Function code 4 •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 16 +X 15 +X 2 +1) is used.
Functions CRC-16 Calculation Example CRC-16 calculation CRC *1 CRC =FFFFh *1 CRC register (2 bytes) Target data Exists CRC *1 = CRC *1 XOR target data All target data completed 8-bit shift Completed Interchange Hi and Lo bytes of CRC *1 CRC *1 = Shift CRC *1 by 1 bit to the right Bits left 0 Overflow bit after shift 1 Completed CRC =CRC XOR A001h *1 *1 Shift by 1 byte against target data •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. 4-81 Function code Function Maximum number of data bytes in 1 message Maximum data number in 1 message 01h Coil status reading 4 32 coils (in bits) 03h Holding register content reading 8 4 registers (in bytes) 05h Writing into the coil 2 1 coil (in bits) 06h Writing into holding register 2 1 registers (in bytes) 08h Loopback test ⎯ ⎯ 0Fh Writing into multiple coils 4 32 coils (in bits) 10h Writing into multiple registers 8 4 registers (in bytes) Hi Lo