G4 Multi Channel Weighing Instrument. PM/DT/HE Technical Manual
G4 Multi Channel Weighing Instrument. PM/DT/HE Technical Manual
G4 Multi Channel Weighing Instrument. PM/DT/HE Technical Manual
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
<strong>G4</strong> <strong>Multi</strong> <strong>Channel</strong> <strong>Weighing</strong> <strong>Instrument</strong>6. CommunicationGeneralThe <strong>G4</strong> <strong>Instrument</strong> has two serial communication ports, one Ethernet port and anoptional fieldbus module.The serial communication ports, the Ethernet port and the optional fieldbusinterface module are used for communication with a control unit.Serial interfaceThe instrument is equipped with 2 serial communication ports: COM1, COM2.COM1 is a RS-232 port and COM2 is a RS-485 portThe COM2 serial communication utilises RS-485 for 2-wire or 4-wire. RS-485 is aninterface working with differential voltages, giving a noise resistant transmission ina network with several units and long distances. The host computer (master) musthave an asynchronous communication port for RS-485, or use a converterfor RS-232 to RS-485 conversion or USB to RS-485.If 2-wire transmission is used, the control unit must be capable of data flowdirection control or utilise a converter for automatic data flow direction control.When 4-wire transmission is used, no data flow direction control is needed.When the RS-232 port is used it’s possible to communicate with one instrument directlyfrom a PC with a RS-232 port without using a converter.Modbus RTU SlaveGeneralAll the <strong>G4</strong> units connected to the network can listen to what is transmitted in thenetwork, but only one unit at a time may transmit. A time-sharing principle isneeded to allow communication in both directions (half duplex).All communication in the network must be initiated by the control unit (master).When the instrument is working together with a master the instrument units are allslaves, only allowed to reply to master commands. As the master has addressed acommand message to a specific slave unit, it listens for the reply during a specifiedtime, before sending next command message.If the reply from a slave unit fails it may be due to:• Mismatch in communication parameters. (baud rate, address, . . )• More than one slave unit has been transmitting at the same time.This can distort the reply message and make it impossible to decode.See ‘6 Communication − Modbus protocol’ section for detailed information ofregister numbering, register content definition, commands etc.More information about Modbus RTU can be found at ‘www.modbus-ida.com’ andmany other places.6-1
Change language