WHA-GW-*
Product Specifications
221981 2011-07
15
Long Tag Emulation
The WirelessHART communication protocol uses the long tag to address devices.
However, long tags are only supported by HART 6 devices and newer devices
(HART 6 = version 6 of the HART communication protocol; current version: HART 7). Older
devices, for example HART 5 devices, have to be addressed by the "Message" field. If a
HART 5 device is connected to the WirelessHART network using a WirelessHART adapter,
the WirelessHART Gateway emulates the long tag with the "Message" field.
2.2.4 Gateway Cache Management
The WirelessHART Gateway caches parameters and dynamic values of the wireless and
wired subdevices and makes them available to the HOST. Some commands are cached by
the Gateway automatically (upon read). Other commands, for example dynamic values, are
only cached if the respective field device publishes them (upon publishing). For more
information on publishing of device values prease refer to the Burst lists section (see
chapter 5.4.3).
The responses to the command requests listed in the following table are cached in the
Gateway. Commands in the same row have an identical response frame and share the
same cache memory. The write commands (17, 18, 22, 51) will never get an immediate
answer, but their response will be cached (caching upon write-confirmation).
Information cached by the Gateway
Status Information Caching
The Gateway chaches the device status byte separately for each wireless or wired device.
The device status will be cached from any type of received message, no matter if from a
wired or wireless device, or if it is a "published" or "normal" response.
The extended device status byte is cached in a similar way, but is available only for
wireless devices.
Cache Command Description
Static
configuration
commands,
cached upon
read or upon
write
confirmation
0, 11, 21 Read unique identifier (associated with tag or long
tag)
12, (17) Read (Write) Message
13, (18) Read (Write) Short Tag, Descriptor, Date
20, (22) Read (Write) Long Tag
50, (51) Read (Write) Dynamic Variable Assignments
Dynamic value
commands,
cached upon
publishing only
1 Read Primary Variable
2 Read Current and Percentage
3 Read All Variables
9 Read Device Variables and Status
33 Read Device Variables
93 Read Trend
48 Read Additional Device Status
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