WirelessHART Fieldgate SWG70
Modbus Interface
E Hauser
119
16.2
Rules for mapping
16.2.1 Automatic mapping of analog devices (HART CMD 3)
Each HART device is mapped into 12 consecutive Modbus input registers. The order of HART
device mapping starting from register 13 is the same as the order of the sub-device identity
summary (returned by HART CMD84). For example, the HART device with the sub-device
index=1 is mapped starting at register 13. The device with the sub-device index = 2 is
mapped starting at register 25, and so on.
To find out the starting register reference address of a certain sub-device, use the following
formula:
• SMIR = 12*(SDI-1)
• SMIR: is the starting Modbus input register of the associated HART device
• SDI: is the sub-device index value.
The following table shows an example of the mapping of the first two HART devices, i.e. the
ones associated with SDI=1 and SDI=2. The assigned Modbus registers can be viewed in the
Input Status and Input Register dialogs. See Chapter 10.3.3 "Input Register" on page 75.
Example of Modbus
mapping of HART CMD 3
Modbus Specific Status
HART Device Status
Reference
address
Modbus RTU
Format:
Sub-device
index
300013 300014 AI
Primary variable (loop current, mA unit)
32-bit floating
point
1
300015 300016 PV
Primary variable (device-specific unit)
300017 300018 SV
Secondary variable (device-specific unit)
300019 300020 TV
Ternary variable (device-specific unit)
300021 300022 QV
Quaternary variable (device-specific unit)
300023 –
ModStat Modbus Specific Status
16-bit unsigned
integer
300024 –
DevStat
HART Device Status
300025 300026 AI
Primary variable (loop current, mA unit)
32-bit floating
point
2
300027 300028 PV
Primary variable (device-specific unit)
300029 300030 SV
Secondary variable (device-specific unit)
300031 300032 TV
Ternary variable (device-specific unit)
300033 300034 QV
Quaternary variable (device-specific unit)
300035 –
ModStat Modbus Specific Status
16-bit unsigned
integer
300036 –
DevStat
HART Device Status
Bit
Parameter
Description
0x01 (LSB)
Cache validity
Set to 1 when the HART CMD 3 cache of the device is empty.
0x02 (LSB)
Identification ongoing
Set to 1 when the gateway is performing a device identification
procedure.
0x04 (LSB)
Device off-line
Set to 1 when the device is offline
Bit
Parameter
Description
0x80
Device malfunction
Device in the network has malfunctioned
0x40
Configuration changed
Configuration of a device in the network has changed
0x20
Cold start
Device in the network has cold start flagged
0x10
More status available
Device in the network has more status available flagged
0x08
Loop current fixed
Loop current of a device in the network is fixed to 4 mA
(multidrop mode)
0x04
Loop current saturated
Loop current of a device in the network above 20 mA
0x02
Non-primary variable out of
limits
SV, TV, QV of a device in the network is out of limits
0x01
Primary variable out of limits PV of a device in the network is out of limits