WirelessHART Fieldgate SWG70
A Appendix: Modbus Interface
Hauser
95
A.2.2
Digital input/output devices
There is no automatic mapping of the Input Status registers: the user must generate the mapping
table either semi-automatically or manually.
• A semi-automatic mapping will duplicate the values entered under the "Generate" tab for all
devices in the network, irrespective of device type
• A manual mapping allows the table to be built up for each individual device (recommended)
Discrete devices publish their values by bursting HART CMD 64386. This tells Fieldgate SWG70
how many discrete values a device is publishing as well as the index of the first discrete value. A
maximum of 256 discrete values can be mapped for each device. At the moment, Fieldgate SWG70
does not map the status of the device.
Each discrete value is published as a UNIT16. Fieldgate SWG70 first splits the data into two bytes
then reserves 8 registers for each byte, i.e. one for each bit.
• The
Least Significant Byte
(x) maps Bits 0 - 7 of the value with Index x
• The
Most Significant Byte
(x) maps Bits 8 - 15 of the value with Index x
The Index "x" is not determined by the position of a discrete value in the device’s burst list, but by
its position in CMD 64385. For example, if the 1st and 4th discrete variables are selected in the
device’s burst list, the corresponding indices will be "0" and "3". Assuming that all bytes are of
interest, the user must enter the following lines:
• Tag Device 1
Least Significant Byte
0
Tag Device 1
Most Significant Byte
0
Tag Device 1
Least Significant Byte
3
Tag Device 1
Most Significant Byte
3
The following (manual) mapping table results:
When Fieldgate SWG70 receives CMD 64386, it checks whether the variables have been mapped,
then enters the associated information. Any values that are not mapped are discarded.
Reference address
Device
Discrete Variable
Bit
Byte (Variable Index)
100001
Device 1
Variable 1
Bit 0
LSB (0)
100002
Device 1
Variable 1
Bit 1
LSB (0)
...
100007
Device 1
Variable 1
Bit 6
LSB (0)
100008
Device 1
Variable 1
Bit 7
LSB (0)
100009
Device 1
Variable 1
Bit 8
MSB (0)
100010
Device 1
Variable 1
Bit 9
MSB (0)
...
100015
Device 1
Variable 1
Bit 14
MSB (0)
100016
Device 1
Variable 1
Bit 15
MSB (0)
100017
Device 1
Variable 4
Bit 0
LSB (3)
...
100025
Device 1
Variable 4
Bit 7
LSB (3)
100026
Device 1
Variable 4
Bit 8
MSB (3)
...
100032
Device 1
Variable 4
Bit 15
MSB (3)
...
Summary of Contents for Fieldgate SWG70
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