DL8000 Preset Instruction Manual
Revised February-2016
Modbus Communications
B-7
B.3 Modbus History
Communications functionality in the DL8000 allows you to retrieve the
Periodic/Hourly and Daily history values and Event/Alarm records
through Modbus Protocol using Function Code 03. Each historical
record contains a time and date stamp on all of the history archives or
values for which you have configured the Register Number.
The system uses the Modbus Function Code 03 and the History Archive
Register to collect the archived data. Two separate Modbus registers
indicate the current Hourly and Daily history index. You configure these
on the Modbus Registers screen as the Hourly History Index Register
and the Daily History Index Register for the segment being referenced
(subtract 1 to get the last archived values). These indexes identify the
current history archive at which data is to be logged.
When the DL8000 receives a Function Code 03 request referencing the
Periodic History Index (commonly register 7161) or Daily History
Index (commonly register 7160), the host interprets the value returned
as an index into the specified history log. The host reads the indexes and
then compares the index to the last polled history index (which the host
maintains) to decide whether to request history.
If the host decides to request history, the reply message contains the
date and time stamp and historical values configured for the specified
register for that index.
For the DL8000, the response message contains two floating point
values for the time and date stamp of the history archive (time stamp =
HHMM and date stamp = MMDDYY) and floating point values for
each of the defined history points for that History Archive Register. The
history date stamp uses the current year and
does not
figure the number
of years since 1980. For example, if the current year is 2007, the year
(YY) for the date stamp would be
07
. The DL8000 maps history
collection on the Modbus History Table.
Table B-3
summarizes the function calls and their associated register
and data fields.
Table B-3. Modbus History, Event, and Alarm Functionality
Function
Code
Register Field
Data Field
Description
03
32 - Event/Alarm
Register
Ignored
1
Response contains Event and Alarm records
2
. Maximum
number of bytes returned is 240 (12 records of 20 bytes
each). Events are returned before Alarms are returned. See
Table A-4
for the displayed format.
05
32 - Event/Alarm
Register
Ignored
After Events and Alarms have been returned, an
acknowledgment occurs so that the same Events and Alarms
are not returned on the next request.
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