Allen-Bradley 1404-M4, Руководство пользователя

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Publication 1404-UM001D-EN-E - October 2004
7-12 Data Logging
Reading Data from the Trend Log
To read the Trend Log, use the indexed read method. A write to
Table A.21 selects which trend log record is read next. There are a
number of auto-increment and manual-increment options that may be
selected by writing to the
Read-back Mode element in Table A.21:
0. Auto-increment / start at beginning: Start at the oldest log record
and index to the next record after each read of the results table
1. Auto-increment / start at end: Start at the newest log record and
index to the next record after each read
2. Auto-decrement / start at end: Start at the newest log record and
index to the previous record after each read
3. Point to the oldest log record
4. Point to the newest log record
5. Index to the next record after each read of the results table
6. Index to the previous record after each read
Only mode 0, 1 and 2 are supported by DF1 and Remote I/O
communications. In modes 0, 1 and 2 the client need only read the
results table repeatedly until the entire Trend Log is read. In modes 3
through 6 the client must alternate writes to select the next read-back
record with reads of the results table. You may obtain the number of
records in the Trend Log by reading Table A.21, elements 7 and 8. The
number of records is (element 7) * 1000 + (element 8).
Only the following elements are needed during a record-selection
write:
•
Password: -1
•
DeviceNet unique write identifier: as applicable
•
Reserved words: must be 0
•
Read- back mode: see above