Power Electronics SD 300 Series, Getting Started Manual

Page: 226 / 354

SD300 POWER ELECTRONICS
224
MODBUS COMMUNICATION
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:
Modbus
Address
Modbus
Function
Code
Starting Data
Address
(44622)
Registers
Number
CRC-16
0x0A 0x03 0x0120D 0x0001 0x2493
Suppose that instantaneous current of the equipment is 8.2 A. (Modbus
value 82 decimal = 0x52 Hexadecimal). The answer of the slave will be:
Modbus
Address
Modbus
Function
Code
Bytes
Number
Data (address
20) (=110)
CRC-16
0x0A 0x03 0x02 0x0052 0x9C78