KROHNE ALTOSONIC V Modbus EN - Manual (Page 5)

ALTOSONIC V
ModBus Manual 0300 rev07 E 7.30855.35.00 Page 5 of 64
1 INTRODUCTION TO MODBUS
From this point in the manual the following abbreviations are used for the ALTOSONIC-V system:
UFS-V: Ultrasonic Flow Sensor (primary flow meter body)
UFC-V: Ultrasonic Flow Converter (5 converters)
UFP-V: Ultrasonic Flow Processor
Introduction to Modbus
For communication with host systems the flow controller emulates a Modbus compatible controller.
The Modbus protocol defines a message structure that controllers will recognise and use, regardless
of the type of network over which they communicate. It describes:
•
the process a controller uses to request access to other devices,
•
how it will respond to requests from the other devices, and
• how errors will be detected and reported.
Controllers communicate using a master-slave principle. Only the master can initiate transactions
(requests), and only the addressed device responds. In case of a broadcast request none of the slaves
will respond.
The Modbus request consist of:
•
an address,
• a function code defining the requested action,
•
data (if necessary for the requested function), and
•
error check for testing the integrity of the message.
The slave’s response contains:
•
the slave address,
•
data conform the request type, and
• error check.
If the data integrity test fails, no response is sent back.
If a request cannot be processed an exception message is returned.