Emerson Micro Motion 3711, Руководство по конфигурации и использованию, Страница: 153 / 234

Configuration and Use Manual 145
Modbus Interface
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12.5.4 Modbus date and time formats
Two different formats are available for date and time values:
For both formats, the datestamp uses the current year, with no modifications. For example, for
calendar year 2005, the YY value is 05. Note that this is different from the YY value in event and
alarm log data.
12.6 Accessing Model 3711 data via the Modbus interface
This section contains information required for coding the host Modbus program.
12.6.1 Register addresses
Depending on the host that will be used to communicate with the transmitter, the host program may
need to subtract 1 from the starting address of the register. Refer to your host documentation to know
if this applies to you.
12.6.2 Accessing history data
The Model 3711 provides special support to allow Modbus host programs to access history data.
History data is stored in two databases: standard history and extended history. The specific values
stored are configurable. Standard history is recorded at three different intervals (typically minute,
hour, and day). Extended history is recorded at a single user-specified interval. See Chapter 8 for
more information on history structure and configuration.
To access history data, a Modbus host program must perform these steps:
1. Send a function code 03 request, referencing the desired index register in the data field (see
Table 12-7).
2. Read and interpret the reply as an index into the specified history log. In other words, the
response contains a pointer to the most recent history record.
3. Compare the returned index to the last polled history index and decide whether or not to
request history.
4. If history is desired, request a history record using Function Code 03. In the data field,
reference the desired history register and the corresponding index value (see Table 12-7). The
history record can contain multiple history points, depending on history access registers
configuration (see Section 12.6.2).
Note: You can request older history records by changing the value in the data field.
Table 12-6 Modbus date and time formats
Format Date Time
Standard MMDDYY HHMMSS
EFM MMDDYY HHMM