143
SV200 DC Hardware Manual
920-0126A
4/14/2017
9.3 Modbus/RTU Communication
There are two types of communication methods for Modbus, ASCII (American Standard Code for information interchange), and RTU
(Remote Terminal Unit). They are defined based on different bus modulation and demodulation methods. For SV200 DC servo drives,
only Modbus/RTU is supported.
9.3.1 Data Encoding
Big-endian: The most significant byte (MSB) value is stored at the memory location with the lowest address; the next byte value in
significance is stored at the next memory location and so on. This is akin to Left-to-Right reading in hexadecimal order.
For example: To store a 32bit data 0x12345678 into register addresses 40031 and 40032, with 0x1234 defined as MSB, and 0x5678 as
LSB, in big-endian system:
Register 40031 = 0x1234
Register 40032 = 0x5678
When transferring 0x12345678, the first word will be 0x1234, and the second word will be 0x5678.
Little-endian: The most significant byte (MSB) value is stored at the memory location with the highest address; the next byte value in
significance is stored at the next memory location and so on. This is akin to Left-to-Right reading in hexadecimal order.
For example: To store a 32bit data 0x12345678 into register addresses 40031 and 40032, with 0x5678 defined as MSB, and 0x1234 as
LSB, in little-endian system:
Register 40031 = 0x5678
Register 40032 = 0x1234
When transferring 0x12345678, the first word will be 0x5678, and the second word will be 0x1234.
The SV200 drive parameter P-75 (PR) defines the data transfer type:
P-75 (PR) = 5 represents big-endian
P-75 (PR) = 133 represents little-endian
9.3.2 Communication Address
In the network system, each drive requires a unique drive address. Only the drive with the matching address will respond to the
host command. In a Modbus network, address “0” is the broadcast address. It cannot be used for an individual drive’s address.
ModbusRTU/ASCII can set the drive address from 1 to 31.
9.3.3 Communication Baud Rate And Framing
SV200 DC servo drives have fixed communication data framing: 8 data bits, one stop bit, no pairty.
The drive parameter P-77 (BR) defines the communication baud rate.
In serial communication, the change of baudrate will NOT take effect immediately, it will ONLY take effect at the next power up of the
drive.
1: 9600bps
2: 19200bps
3: 38400bps
4: 57600bps
5: 115200bps
