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Configuration via Web Interface
MODBUS Parameters
For a detailed overview of the relationship between the configuration options in the DTM or web
interface and the data in the WirelessHART gateway, see Figure 5.19 on page 63.
MODBUS Implementation
The MODBUS implementation maps HART dynamic input variables to MODBUS input
registers and uses input registers to provide device-related status information. The MODBUS
implementation is based on the following assumptions:
■
The HART CMD 3 dynamic variables are used for MODBUS mapping.
■
For MODBUS access, CMD 3 publishing must be enabled for all relevant devices.
■
The WirelessHART gateway caches the relevant CMD 3 information. MODBUS
commands will therefore access the internal memory of the WirelessHART gateway.
■
MODBUS input registers are only supported if they are associated with HART dynamic
input variables.
Parameter
Description
Swap Option
Enables you to select the
Big Endian
or
Little Endian
swap option. Note that
this setting affects both automatic and manual addressing of the MODBUS
registers.
In the following examples a word32 [ 0xABCD ] is stored into MODBUS
registers using different swap options.
Big Endian: no register swap
Registers: Big Endian
Source bytes: [ 0xABCD ]
Target bytes: reg_0: [ 0xAB ] reg_1: [ 0xCD ]
Little Endian: register swap
Registers: Little Endian
Source bytes: [ 0xABCD ]
Target bytes: reg_0: [ 0xCD ] reg_1: [ 0xAB ]
Addressing
Method
Enables you to select
Auto
or
Manual
addressing of the MODBUS registers.
Note that the
Manual
option also includes semi-automatic addressing.
■
If
Auto
addressing is enabled, the submenus
Input Status
and
Input
Register
are disabled and you cannot edit the MODBUS mapping
manually. The mapping is created automatically for all devices of the
Operating Modes
list. If new WirelessHART devices appear in the
WirelessHART network, they are automatically added to the
Operating
Modes
list, and the mapping will also be added automatically. See
chapter 5.5.5.
■
If
Manual
addressing is enabled, you can use the submenus
Input Status
and
Input Register
to set up the MODBUS mapping manually or semi-
automatically for all devices of the
Instrument List
. If a new
WirelessHART device joins the WirelessHART network, it is added to the
Operating Modes
list only. The new device will not appear in the
Instrument List
unless you import the device list from the
Operating
Modes
list. See chapter .
Read
Modbus
Registers
Mode
Enables you to define the read mode for the MODBUS master. You can select
between
Input and Holding
and
Input Registers only
. If you select
Input
and Holding
, MODBUS masters that do not support the reading of input
registers can read through the holding registers.
Table 5.15 MODBUS Parameters
Tip
If you replace a WirelessHART gateway with firmware version 2.4 or older, we recommend that
you select
Auto
from the
Addressing Method
drop-down list.