lib/rtc.txt
author mjsousa <msousa@fe.up.pt>
Thu, 10 May 2012 16:09:50 +0100
changeset 552 3c39d80fdede
parent 400 093b72cd2ac3
child 885 b2604fc6d25c
permissions -rw-r--r--
Add high level comments.
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(****************************************************************
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              RTC - Real-time clock
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Q is a copy of IN.
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When IN = FALSE, CDT is the current date and time as set by the
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PLC driver.
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When IN changes from FALSE to TRUE, PDT is stored. As long as IN is
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TRUE, CDT is equal to PDT + the amount of time since PDT was loaded.
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****************************************************************)
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FUNCTION_BLOCK RTC
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   VAR_INPUT
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     IN : BOOL;                  (* 0 - current time, 1 - load time from 
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PDT *)
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     PDT : DT;                   (* Preset datetime *)
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   END_VAR
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   VAR_OUTPUT
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     Q : BOOL := FALSE;          (* Copy of IN *)
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     CDT : DT;                   (* Datetime, current or relative to PDT *)
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   END_VAR
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   VAR
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     PREV_IN : BOOL := FALSE;
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     OFFSET : TIME;
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     CURRENT_TIME : DT;
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   END_VAR
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   {__SET_VAR(data__->,CURRENT_TIME,__CURRENT_TIME)}
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   IF IN
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   THEN
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     IF NOT PREV_IN
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     THEN
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         OFFSET := PDT - CURRENT_TIME;
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     END_IF;
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     (* PDT + time since PDT was loaded *)
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     CDT := CURRENT_TIME + OFFSET;
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   ELSE
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     CDT := CURRENT_TIME;
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   END_IF;
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   Q := IN;
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   PREV_IN := IN;
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END_FUNCTION_BLOCK
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