Power Electronics SD700 Series User Manual

SD700
POWER ELECTRONICS
62
MODBUS COMMUNICATION
5. MODBUS COMMUNICATION
5.1. Supported Modbus Function Codes
Serial communications protocol provided by SD700 drive adheres to Modbus Industrial standard
communications protocol of Modicon. The drive uses reading and writing functions between all of the
functions that exist in Modbus protocol. The used functions by the drive are the following ones:
Function
Description
Registers Number
3
Registers Reading
120
16
Registers Writing
120
The implementation of this function code in the drive allows reading up to 120 registers into a
Parameters Group in a frame. If you want to access to a consecutive memory registers, but
belonging to different groups, you should access in so many frames as groups are involved.
5.1.1. Modbus Function Code Nº 3: Registers Reading
This function code allows the Modbus controller (master) to read the content of the data registers
indicated in the drive (slave). This function code only admits unicast addressing. Broadcast or
groupcast addressing are not possible with this function code.
The implementation of this function code in the drive allows reading up to 120 registers with
consecutive addresses of the drive in a single frame.
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 one:
 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 one is the default length of all of the
registers that form the SD700.

Power Electronics SD700 Series Specifications

General

Brand	Power Electronics
Model	SD700 Series
Category	Inverter
Language	English