22
1981
2011
-0
7
84
WHA-GW-*
Operation
6.5.2
Modbus Mapping Description
Figure 6.15Parameter > Wired Communication > Protocols > Modbus
Mapping rules
Each HART device is mapped into 12 consecutive Modbus input registers. The first device
is mapped starting at register 30013, the second starting at register 30025, and so on. The
input registers can be read using Modbus function code 04 (Read Input Registers).
The order of HART device mapping starting from register 30001 is the same as the order of
the HART devices returned by the gateway command 84 (HART CMD 84, Read sub-device
identity summary). For example, the HART device that you can read by using CMD 84 with
the sub-device index = 1 is mapped starting at register 30013. The device that you can
read by using CMD 84 with the sub-device index = 2 is mapped starting at register 30025,
and so on.
The information about the WHA-GW itself is mapped into registers 30001 to 30012.
To find out the starting register of a certain sub-device, use the following formula:
SIR = 30001 + 12*(SDI)
"SIR" being the starting input register of the associated HART device and "SDI" being the
CMD 84 sub-device index value.
The following table shows the exemplary mapping of the first two HART devices, i.e. the
ones associated with SDI = 1 and SDI = 2.
Note!
The Modbus starting register of each device in the WirelesHART network is displayed in
the DTM (
Parameter > Wired Communication > Protocols > Modbus
, see chapter
5.5.4).
