S7 300 stl programming

[FernandoJose]

I'm new in STL programming, today I was checking some example codes and found this:

L 1
L QB 4
SLW
T QB 4
SET
SAVE
CLR

I do not know the final result in QB4, can someone help me?

 

[dwoodlock]

I'm not an STL expert, but I will venture a guess.

Basically you are shifting output byte 4 by 1 every time this code executes.

Load 1 into Accu1
Load QB4 into Accu1, which moves 1 to Accu2
Shift all the bits in Accu1 the integer that's in Accu2
transfer the result to QB4

If QB4 starts as 0000_0010

after the code executes once it will be 0000_0100.

hopefully this helps

 

[FernandoJose]

Thanks you for your quick answer. So every time I use SLW first I load de number of bits that will be shifted, and then I load the data that will be shifted right?

 

[dwoodlock]

There are actually more than one way that you can structure the instruction, but that will work.

I am a little confused about the fact that the W in SLW stands for Word and we are only assigning a byte, but perhaps someone who has a better understanding or experience with the instruction can enlighten us.

 

[Lare]

STL don't check what type variables are

 

[Jeebs]

Thanks you for your quick answer. So every time I use SLW first I load de number of bits that will be shifted, and then I load the data that will be shifted right?

There are 2 ways you can do it.
If it's a fixed number of bits it needs to be shifted, you can do:

L QB4
SLW 1   // Shifts ACCU1 1 bit, you can do 4, 7, 8, etc.
T QB4

If you want to change the number of bits that you want it to shift, you can do:

L MB1   // Contains the nr of bits you want ACCU1 to shift
L QB4
SLW     // Shifts ACCU1 x amounts of bits
T QB4