X20 system modules • Analog input modules • X20AI2438
X20 system User's Manual 3.10
217
PvSampleTime
The registers return the timestamp for when the module reads the current channel mapping. The values are pro-
vided as signed 2-byte or 4-byte values.
Data type
Values [µs]
INT
-32768 to 32767: Nettime timestamp of the current input value
DINT
-2,147,483,648 to 2,147,483,647: Nettime timestamp of the current input value
This refers to the point in time when the HART master receives the slave's response. This is a way to check whether
new HART information has been read since the last X2X cycle.
Information:
The cycle times of a HART network are relatively long so that it is not possible to reliably determine
when exactly the measured value is retrieved with just this information.
PvNodeComStatus
The "PvNodeComStatus" registers return information about whether a value that has been read is valid. According
to the HART specification, this type of status register consists of two parts. The high byte stores the "response
code" and the low byte the "field device status". This makes it possible to check the current status of a read process
variable.
The "PvNodeComStatus" register can be checked before further processing information in temporary storage. If
the current value is 0x0000, an error was not detected during the HART transfer and the information from the
checked node can be used. If a different value is present, the situation in the HART network should be checked.
This can be done using an extension register, for example.
Data type
Values
UINT
See bit structure
Bit structure:
Bit
Name
Information
0
Digital measured value okay
0
Quality - Node information 2…n
1
Measured value outside the permitted range
0
Digital measured value okay
1
Quality - Node information 1
1
Measured value outside the permitted range
0
Parameter okay
2
Limit violation
1
Invalid measured value(s) or encoder supply value
0
Normal value change/fluctuation
3
Static analog signal
1
Constant analog value of Node 1 slave
0
Not available
4
Additional status information
(only supported by a few slaves)
1
Available (only using FlatStream command #48)
0
Normal operation
5
Reboot
1
Field device restarts
0
Unchanged
6
Device ID
1
Changed
0
Measured value okay
7
Device error
1
Questionable measured value information
8-14
Response code, if relevant
See coding (HART-specific)
0
Error-free communication (response code irrelevant)
15
Error - Communication
1
Faulty communication (response code relevant)
HART-specific response code (excerpt):
0x82 … Receive buffer overflow
0x88 … Incorrect checksum
0x90 … Faulty protocol structure
0xA0 … Overrun
0xC0 … Parity not allowed
0xFF … Timeout
If a HART communication error occurs, the response code is written. Bit 15 is
always set.
Retrieving information that has been read
After the node data has been transferred to the module registers, the information can be retrieved from the module.
A separate register in the module is implemented for each piece of information.
Summary of Contents for X20 System
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