CERUS CI-007-P2, Installation, Programming Operation, & Maintenance Manual

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Chapter 11 – Modbus-RTU Communication
10-1
CHAPTER 10 - MODBUS-RTU COMMUNICATION
10.1 Introduction
VFD can be controlled and monitored via communication by the BMS, PLC or other master module.
Drives or other slave devices may be connected in a multi-drop Modbus-RTU network with up to 31 units
and may be monitored or controlled by a single master control device.
When master sends Write Request to VFD address 0X00, all VFDs perform write action but do not return
acknowledge response. This is used to drive multiple VFDs at the same time via Modbus-RTU
communication on RS-485 port.
10.1.1 Connection guide for Modbus-RTU communication with PC , PLC and RS-232C/485
Note: The repeater is used for long-distance communication or high noise environment.
10.2 Specification
10.2.1 Performance specification
Item Specification
Transmission form Bus method, Multi-drop Link System
Applicable VFD P series
Max. drives quantity 31
Transmission distance Max. 4,000ft (up to 2,500ft Recommended)
Recommended wire 0.75mm
2
(12AWG), Shield Type Twisted-Pair Cable
10.2.2 Hardware specification
Item Specification
Installation Use C+ and C- terminals
10.2.3 Communication specification
Item Specification
Communication speed 38,400/ 19,200/ 9,600/ 4,800/ 2,400/ 1,200 bps selectable
Communication system Half duplex system
Character system Binary (8 bit)
Stop bit length 1 bit
Error check(CRC16) 2 bytes
Parity bit None
Protocol supported Parameter Read/Write, Monitoring parameter register/execution
Broadcasting
PC
PC PC
PC
VFD
#1
VFD
#2
VFD
#n
USB-485 or
RS-232C-485
Converter
Repeater