How to use Up/Down Counter in Step 7?

plcnoviceguy · Mar 6, 2007

I need to know how to use the Up/Down counter in Step 7 STL.

Just need the basics IE: How to call to it in STL and how to increment/decrement. Thanks!

dchartier · Mar 6, 2007

Hello plcnoviceguy;

I found that the easiest way of understanding the STL functionnalities, for a beginner, is to write the code in LAD, study all the inputs and outputs of the block I want to understand (use the F1/help functionnalities or the program manual), and then translate the block from LAD to STL (View menu in the LAD/FBD/STL editor).
Something like this:

Hope this helps,
Daniel Chartier

10BaseT. · Mar 7, 2007

plcnoviceguy said:
I need to know how to use the Up/Down counter in Step 7 STL.

Just need the basics IE: How to call to it in STL and how to increment/decrement. Thanks!

As a novice , I would call it in ladder first , you may find it easier to understand compared to STL .

This is yet another case where there is absolutely nothing to be gained by using STL .

L D[AR2P#0.0] · Mar 7, 2007

Note that the Siemens in-built counter counts from 0 to 999

Also available is SFB2 which counts in the range -32768 to +32676

Jeebs · Mar 7, 2007

As L D[AR2,P#0.0] said, the siemens counters only count to 999, but it is very easy to create your own counters that will count to 2.147.483.647ish

And as said above, of you don't know it in STL, try it in LAD, convert it to STL and try to figure it out. And use the help files. There is alot of nice info hidden in there.

plcnoviceguy · Mar 7, 2007

Thanks guys.

userxyz · Mar 7, 2007

Maybe a little question...

10BaseT. said:
As a novice , I would call it in ladder first , you may find it easier to understand compared to STL .

This is yet another case where there is absolutely nothing to be gained by using STL .

I agree, but I do have a question.

Sometimes we want to avoid timers and counters by doing this:

For Counters:

A I 0.0
FP #mem1
JCN PRES
L #COUNT
L 1
+I
T #COUNT
PRES: A I 0.1
FP #mem2
JCN DECR
L 15
T #COUNT

DECR: A I 0.2
FP #mem3
JCN END
L #COUNT
L 1
-I
T #COUNT
END: L #COUNT
T MW 10

For Timers:

A I 0.0
A M 0.5 // pulse every second
FP #mem1
JCN OUT
L #TimeV
L 1
+I
T #TimeV
OUT: L #TimeV
L 10
>=I
= Q 0.0
RES: A I 0.1
JCN END
L 0
T #TimeV
END: NOP 0

// After 10s, Q0.0 is high
// M0.5 is a bit of the clock memorybyte in the CPU

Is this good or bad, and why ?

Giz99 · Mar 7, 2007

Just add or subtract 1 in conjunction with a one shot to a double integer. It is not elegant but it is simple and works.

10BaseT. · Mar 7, 2007

Well I posted "my" solution a while back , I use the last cycle time generated by OB1 as the time base for a roll your own timer - you can also change the time on the fly , and lift the elapsed time as well if required - take a look , you should be able to find it . There is a slight flaw in the accuracy ( 1 cycle time over) - but within a few milliseconds is enough for most applications .
From the outside the block looks like an IEC timer .

How to use Up/Down Counter in Step 7?

plcnoviceguy

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L D[AR2P#0.0]

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