Solartron Mobrey 7828, Техническое руководство

Страница: 84 / 110

Modbus Communications 7828 Density Transmitter Technical Manual
D-2
78285000_AA
D.2 ACCESSING MODBUS REGISTERS
Any device which can drive the RS485 interface on the 7828 can, in theory, access the
Modbus registers. In practice, some sort of user interface is required to simplify the
process.
ADView, which is distributed with the 7828, offers several ways of accessing the registers.
Board Configuration: A graphical interface for viewing and setting the main
configuration parameters of the 7828.
Direct access to registers is not offered.
Register Read/Write
This tool provides a simple window from which to read and
write to named and numbered registers. When you write to
a register, you are presented with a set of allowable values
from which to choose. Thus the tool is only useful for
communicating with Solartron transmitters.
This is the simplest and most foolproof way of directly
accessing the registers. Section 4 gives full details.
Direct Communications This is another tool which allows you to compose a
sequence of data to be transmitted to/from the Modbus.
This can be used to communicate with any Modbus device,
providing that you know the register addresses, data
format, indices, etc.
The composition of the data is entirely up to the user,
although the tool does compute and insert a checksum.
Only those well versed in the use of Modbus protocol
should attempt to use this facility.
It is mainly designed for testing Modbus transmissions
which are subsequently to be used in an application specific
environment.
A worked example of using this tool is given in section D.7.
D.2.1 ESTABLISHING MODBUS COMMUNICATIONS
If the transducer Slave address or the values of Registers 47 and 48 are not known,
Modbus communications cannot be carried out successfully, and it will be necessary to
establish the current values in these items. If you are using ADView, you can search for
the addresses of all connected slaves, and then interrogate the appropriate registers for
each one.
If you are not using ADView, section D.6 gives a procedure which will enable you to
ascertain this information.