Inovance MD520 Series - Page 29

Modbus Communication
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Table 3–4 Data frame fields
Frame header (START) Idle time longer than the transmission time of 3.5 characters
Slave address (ADR) Communication address range: 1 to 247
Command code (CMD) 03: Read slave parameters; 06: Write to slave parameters; 10:
Multi‑write to slave parameters
Parameter address (H) Internal parameter address of the AC drive, in hexadecimal
format; parameter type or non‑ parameter type (such as the
running status and running command). For details, see the
address definition.
Low‑order bytes follow high‑order bytes during transmission.
Parameter address (L)
Number of parameters
(H)
Number of parameters read in this frame. 1 indicates that one
parameter is read. Low‑order bytes follow high‑order bytes
during transmission.
This field is unavailable because this protocol allows only one
parameter to be modified at a time.
Number of parameters
(L)
Number of data bytes Data length, which is twice the number of parameters
Data (H) Response data or data to be written. Low‑order bytes follow
high‑order bytes during transmission.
Data (L)
CRC lower bits Check value: CRC16 check value. Low‑order bytes follow high‑
order bytes during transmission.
For details about the calculation method, see the description of
CRC in this section.
CRC higher bits
END
Transmission time of 3.5 characters
CRC check:
The cyclical redundancy check (CRC) adopts the RTU frame format. A Modbus
message includes a CRC‑based error‑check field, which checks content of the entire
message. The CRC field is two bytes, containing a 16‑bit binary value. It is added to