Eurotherm 7000 Series, Руководство пользователя

Страница: 55 / 69

Digital Communication
7300A User Manual 6-2
Chapter 6 DIGITAL COMMUNICATION
6.1.GENERAL
Digital communication option can :
• control 7300A thyristo units
• monitor all operating parameters via the Supervisor.
6.1.1. Exchange type
Message are exchanged in ‘Master/Slave’ mode.
The digital communication option always operates as a slave, with the supervision
system or PLC as Master. All exchange comprise a request from the Master and an answer
from the slave (except in broadcast mode).
6.1.2. Communication protocol
The Modbus® RTU communication protocol is used.
Communication complies with the specifications given in ’GOULD MODICON Protocol
Reference Guide PI-MBUS-300 rev J’.
6.1.3. Transmission
Transmission standard : RS485, 2 wires. The transmission frame uses binary characters.
Format of each character :
• 1 start bit
• 8 data bits
• 1 stop bit
Transmission is asynchronous.
Two transmission speeds are available : 9,6 or 19,2 kbaud.
The speed can only be selected by the microswitch SW8 on the interface.
6.1.4. Parameters status
The status of a parameter may be Read, Read and Write or Memorised Read/Write :
• Read only parameters are labelled ‘R’
• Read and Write parameters are labelled ‘R/W’
• Memorised Read and Write parameters are labelled ‘R/W/M’
6.1.5. Power failure
If the power supply ‘AUX2’ fails, the interface stops communicating and the output is set to zero.
When power is restored, the interface enters ‘waiting for communication’ state.