Shortcut to detect Neg Edge in a Word

Step 0: Initialize saved value of word to 16#0000 (only once)

Step 1: IF value of word < saved value of word THEN reset output

Step 2: Save current value of word to persistent memory (preferably to an FB static or DB tag)

Program it#

Hi All,

Is there any shortcut to detect Negative Edge of Any /All bits in a WORD and reset an output? 

Any bit turning OFF (1---->>0) should reset same output...

Regards.

Program it#

Hi 0_Einstein,

Value of saved word is not constant. Let me put it this way, Let's say, each bit in the WORD represents one Fan. Following a command, 16 Fans will turn on sequentially in order with 1-3 seconds delay between any two fans.

The challenge here is, if in the middle of the turning on process, say if 6th fan is switching on and exactly at that time 3rd fan is tripped, the command should reset.

Now for comparison I need a fixed value. How to compare now????

Which command should be reset? Some options are:
a) The starting sequence is cancelled
b) Fan 3 is stopped
c) Fan 6 is not started, freeze starting sequence.
d) Fan 1 and 2 still runs but all others stops.

Why is the edge trigger so important? In other words: why not evaluate the level?

When is there a fault condition for the trip? Is is "healthy" = TRUE or "tripped" = TRUE?

Basics to detect a change in a Word:

// Any bit changed its state
#change      := #nowWord <> #oldWord;

// Any bit changed to TRUE
#changeTrue  := (    #nowWord and not #oldWord) <> 0;

// Any bit changed to FALSE
#changeFalse := (not #nowWord and     #oldWord) <> 0;

// Helper to detect change
#oldWord     := #nowWord;

Does the code piece already help you?

Program it#

Hi 0_Einstein,

Command should be reset means your options (a) & (d).

Fan 1 & 2 still running and all other stops. Sequence is cancelled.

Trip= false state.

Actually I am confused with my #old word and #Now word.

How/When to exchange data between #old word and #now word? Because my #new word is continuously changing..

I am "qwazee". You have replied to my post.

#nowWord is the ever changing data you named #new (see above quote).

#oldWord is used by the code and looks after itself.
It is an internal memory either MW or STAT in an FB or from a DB.
#oldWord is the copy of #nowWord which you called #new.

Attached is a draft design idea for a sequence starter, coded for an S7-1x00 in SCL. It uses the concept of manipulating WORD tags. There is a design "flaw" which I leave for you to notice.

My preference for this application would be to use bit arrays.

Program it#

Hi Qwazee,

Thanks for this help. To make your program working I made changes at 3 places.

1. Expression (NOT #iwHealth and #statoldHealth)<>0. Here I replaced <> with = sign.

2. SHR function replaced with SHL.

3. TIMER definition changed from IEC TIMER to TON timer.

Please elaborate on FINDING out change in bits in WORD. I tired with many examples but your Expression didn't work.

Thank you for correcting my mistakes. I have used your corrections 1 & 2 to modified the original draft. This time I have actually tested it. Find it above.

"Please elaborate on FINDING out change in bits in WORD."
No. First show me what you are doing via screen capture / PDF / sample project.