Appendix 2: Rs485 Communication Protocol - Veichi AC100-T3-1R5G Manual

AC100 HIGH-PERFORMANCE VC INVERTER MANUAL

9.2 Appendix 2: RS485 Communication Protocol

Introduction
●
The AC100 series frequency inverter is equipped with the RS485 communication interface and
communication protocol of international standard is adopted for master-slave communication. Users can realize
centralized control by PC/PLC, upper machine, mAC80Cn station frequency inverter etc (Setting of the frequency
inverter control command, running frequency, relative function parameters modification, frequency inverter working
state and malfunction information monitoring etc.) to adapt to specific application requirements.
Application Methods
●
1. AC100 series frequency inverter is connected to "single host and multi slave machines" control network with RS485
master line. Slave machine do not response when host machine order with broadcast (slave machine address is 0).
2. AC100 only provides RS485 interface, asynchronous half-duplex. When the communication interface of the external
equipment is RS232, RS232/RS485 converter should be added.
3. This ModBus serial communication protocol defines the asynchronous transfer information content and formats used
in the serial communication, which can be divided into RUT and ASCII mode. AC100 is RTU（remote terminal unit）
mode.
Communication Frame Structure
●
Communication data format is as follows:
The byte composition: Including initiation bit, 8 data bit, check bit and stop bit.
Initiation
Bit1
Bit
One frame message must be transmitted as a continued data flow, and if there is a interval over 1.5 byte before ending,
the receiving equipment will clear the half-baked information. And the next byte will be considered as the address field
of a new frame. Similarly, if the interval between a new frame start-up and the former frame is smaller than 3.5 byte time,
the receiving equipment will consider that it is the continuation of former one frame. Since the jumbled frame, the final
CRC checking value is incorrect, which would lead to the communication mistake.
Standard Structure of RTU Frame:
Frame Start
Slave machine address
Command code
Data area
CRC CHK low-order
CRC CHK high-order
Frame ending
In RTU mode, it always begins with transmission time pause gap of at least 3.5 bytes. The successive order of the
following transmission data domains: slave machine address、operation command code, data and CRC checking bit.
Transmission byte of each domain is hexadecimal 0...9, A...F. Network equipment detects the network bus unceasingly,
including the pause gap time. When receiving the first domain (address information), each network equipment would
carry out decoding to judge whether the byte is sent to itself. When the final byte transmission is completed, there will
be an at least 3.5 bytes transmission time pause gap to indicate that this frame is over. Then a new information
transmission can start.
Bit2 Bit3 Bit4
Transmission time of 3.5 bytes
Communication address:
0～247（decimal）（0 is the broadcast address）
03H: read slave machine parameter
06H: write slave machine parameter
08H: circuit auto-detection
parameter address, parameter number, parameter values
Detecting value: 16 bit CRC Detecting value
transmission time of 3.5 bytes
Bit5 Bit6 Bit7
188
Appendix
t he ModBus
Check Stop
Bit8
bit bit