ProSoft Technology MVI56-AFC - Manual (Page 153)

MVI56-AFC ♦ ControlLogix Platform Events
Liquid and Gas Flow Computer User Manual
ProSoft Technology, Inc. Page 153 of 316
February 25, 2011
Also in these procedures:
a) The expression "AND 0x0000FFFF" means "take the low-order 16 bits of
the result, discarding all other higher-order bits"; it is equivalent to "(non-
negative) remainder upon dividing by 65536" (A traditionally negative
remainder that would result from dividing a negative dividend by 65536
must be made positive by subtracting its absolute value from 65536)
b) The operator ":=" means "assignment"; that is, "assign" the expression on
the right to the object on the left by calculating the value of the expression
on the right and making the object on the left assume that value. The
operator "==" means "is equal to".
c) Words in all caps and the other arithmetic operators have their expected
meanings.
d) Text enclosed in brackets ("[ ]") are comments only.
Procedure (A): Calculate event number from record position.
1 Calculate number of events on file.
events_on_file := ( next_event - oldest_event ) AND 0x0000FFFF
2 Determine whether desired record is on file.
IF ( my_record < 0 OR my_record ≥ events_on_file ) THEN
[record is not on file]
EXIT this procedure
3 Calculate age of desired record.
event_age := ( next_record - my_record )
IF ( event_age ≤ 0 ) THEN
event_age := event_age + number_of_records
4 Calculate event number of desired record.
event_number := ( next_event - event_age ) AND 0x0000FFFF
Procedure (B): Calculate record position from event number.
1 Calculate number of events on file.
events_on_file := ( next_event - oldest_event ) AND 0x0000FFFF
2 Calculate age of desired event.
event_age := ( next_event - my_event ) AND 0x0000FFFF
3 Determine whether desired event is on file.
IF ( event_age == 0 OR event_age > events_on_file ) THEN
[event is not on file]
EXIT this procedure
4 Calculate record position of desired event.
record_position := ( next_position - event_age )
IF ( record_position < 0 ) THEN
record_position := record_position + number_of_records
Procedure (C): Calculate Modbus address of record from record position.
1 Calculate number of events on file.
events_on_file := ( next_event - oldest_event ) AND 0x0000FFFF
2 Determine whether desired record is on file.