Next, a frame is shown where the master tries to read the content of 3
registers of a drive where the current used by each phase is. The
information that should be attached in the ask frame is the following:
• Data address of the drive.
• Modbus function code (3 Registers reading).
• Starting Data address.
• Registers number for reading.
• CRC-16 code.
The answer of the drive (slave) should contain the following fields:
• Data address of the slave.
• Modbus function code (3 Registers reading).
• Bytes number for reading.
• Bytes number / 2 registers.
• CRC-16 code.
Each register consists of 2 bytes (2x8bits=16 bits). This is the default
length for all registers.
Example:
Suppose that we want to read the motor current (nameplate data) via
communications. This data corresponds to the parameter G2.13 ‘MTR
CUR=0.0A’. The frame that should be transmitted is:
Suppose that instantaneous current of the equipment is 8.2 A. (Modbus
value 82 decimal = 0x52 Hexadecimal). The answer of the slave will be:
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