Using arrays or bytes to set multiple outputs in Structured Text

Question

I am fooling around in TwinCAT3 trying and getting familiar with ST. I now have a simple question.

Say I have 8 LEDS. Each assigned to an output 1-8. Now I want to be able to send in a byte looking like such: 10101010. Lets call that variable to hold that byte setOUTPUTS. Would I initalize setOUTPUTS as follows to hold that?

bsetOUTPUTS := BYTE;

After I initialize that variable, how could I loop through it to set each LED to the corresponding bit?

For instance: setOUTPUTS = 10001000, how would i loop through setOUTPUTS variable to set LED 8 and LED 4 ON , while leaving the others OFF.

IF this is not possible, what is the alternative way using arrays?

Thanks!!

are you programming in Codesys?

mrsargent
– mrsargent

2016-12-16 16:32:01 +00:00
Commented Dec 16, 2016 at 16:32 — mrsargent
– mrsargent, Commented Dec 16, 2016 at 16:32
No in TwinCAT environment

youngEngineer
– youngEngineer

2016-12-19 17:37:48 +00:00
Commented Dec 19, 2016 at 17:37 — youngEngineer
– youngEngineer, Commented Dec 19, 2016 at 17:37

mrsargent · Accepted Answer · 2016-12-16 16:46:32Z

1

To initialize a byte you would

setOUTPUTS : BYTE:=86; (* equiavlent to 01010101  *)

you can set the outputs based on a bit as follows

out1 := setOUTPUTS.0;  (* bit 0 of byte *)
out2:=setOUTPUTS.1;  (* bit 1 of byte *)

you might think that you could do something like to loop through the bits in the byte

FOR i:=0 TO 8 BY 1 DO
(* out is an array of outputs *)
out[i] := setOUTPUTS.i;
END_FOR

but unfortunately you are unable to do this. As far as I know setting them individually is the only way to accomplish this.

answered Dec 16, 2016 at 16:46

mrsargent

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pboedker · Accepted Answer · 2016-12-19 07:32:59Z

1

You can compare each bit of your setOutputs variable with a bit that is shifted through the length of setOutputs:

FOR i := 0 TO 7 DO
  out[i] := setOutputs AND SHL(1, i);
END_FOR;

answered Dec 19, 2016 at 7:32

pboedker

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3 Comments

mrsargent Over a year ago

Good answer. I didn't think about that. +1 for you.

youngEngineer Over a year ago

Would out[i] be the array/enum of 8 LEDS? and does SHL mean shift-left by 1? Thanks!

pboedker Over a year ago

out[i] is an array that could be mapped to 8 individual LEDs. SHL(n,i) will shift the number n, 'i' times to the left.

Stucky · Accepted Answer · 2018-03-21 15:51:12Z

0

I would simply map the bit of "bsetOUTPUTS" to the IO.

Offset 0 means bit 0, offset 1 means bit 1, etc.

So I will link my channel 1 (LED 1) to bsetOUTPUTS offset 0, channel 2 to bsetOUTPUTS offset 1, etc.

answered Mar 21, 2018 at 15:51

Stucky

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