Hi guys,

I have to make a FC that swap the two bytes in a word to convert the hideous Siemens Word addressing to the Mankind word addressing and so I have to swap the two bytes of a word:

W1 is made by B1 and B0 so B1B0

I want that W2 is B0B1

Bit addressing is pretty painful and is a waste of code.

So I though : why not the great ROL ?

W2:=ROL(W1,8)

Can it work ?

Sorry but I cannot test it so I need a quick overview at this...

Davinator

Hi guys,

I have to make a FC that swap the two bytes in a word to convert the hideous Siemens Word addressing to the Mankind word addressing and so I have to swap the two bytes of a word:

W1 is made by B1 and B0 so B1B0

I want that W2 is B0B1

Bit addressing is pretty painful and is a waste of code.

So I though : why not the great ROL ?

W2:=ROL(W1,8)

Can it work ?

Sorry but I cannot test it so I need a quick overview at this...

 For STL....

Davinator

I thought that CAW worked in AWL only

My dear fellow...   STL <<-->> AWL

If you need your solution in SCL, then your solution will work for a WORD.
Just take care not to try doing this for DWORD.
Or simply just do...

MB101 := MB200;
MB100 := MB201;

Will,

thanks, I am not familiar with AWL and I don't wiant to use it.

My solution works also for DWORD, just need to change the ROL amount from 8 to 32 , I think.

It's not clear what you say with those MB since I have a word and I'd like to create an FC under 300 TIA environment

Davinator

Will,

thanks, I am not familiar with AWL and I don't wiant to use it.

My solution works also for DWORD, just need to change the ROL amount from 8 to 32 , I think.

It's not clear what you say with those MB since I have a word and I'd like to create an FC under 300 TIA environment

Some things are best done in STL for the S7-300 and S7-400.

No... rotate will not work for DWORDs.

Which environment are you using? Step7 V5.5 or TIA Portal?
You have direct addressing available to you..
so the MB example is not so useless for showing a concept.

..but no worries - I'm sure you'll get some follow up from the guys.

Cheers.
w

Why ROL won't work for DWORD ?

I have read the TIA example about that and it shows a DWORD

And yes, TIA, not S7

Davinator

Why ROL won't work for DWORD ?

I have read the TIA example about that and it shows a DWORD 

And yes, TIA, not S7

Hi.

You created this thread to share with us a method you discovered to swap bytes for a WORD when coding in SCL. I am sorry for hijacking your thread and focussing on going the step further. Please know it is not for points and not void of malice.

Swapping bytes means that, in case of a DWORD,
16#11223344
is for example transformed to
16#44332211.

Yes, applying ROL or ROR instructions on a DWORD is possible. In context with the theme - Rotating a DWORD will not produce swapped bytes. More explicitly said - a single rotation instruction is not enough to swap bytes as per the example given above.
 
Splitting hairs:
Rotating a DWORD with 32 bit positions, is making a 360° rotation.. not helpful as you end up with what you started with. "S7" relates to the hardware family and has nothing to do with the software.

Back on theme - how about some variations examples?

(1) Using STL


(2) Using SCL.. Cross platform design (also non-Siemens)
^{.......... S7-1500 and S7-1200 already have a SWAP instruction.}


(3) Usage example in SCL

The advantage that you can gain from using SCL, is designing coding that can be ported to other platforms (other CPUs and other brands). It does take some effort at times to get a design that will do the task.. especially if you have to keep the S7-300 in mind.

Even if the above was purely academical.. I hope it expands someone's thoughts in this matter.
w

William ment that with the ROL you can not change endianity of 32 bit var.

In general, I wouldn't break the open doors. I'd write simple 3 STL lines in the FC and then call the FC in a language of my choice.

Davinator

Hi guys,

I have to make a FC that swap the two bytes in a word to convert the hideous Siemens Word addressing to the Mankind word addressing and so I have to swap the two bytes of a word:

W1 is made by B1 and B0 so B1B0

I want that W2 is B0B1

Bit addressing is pretty painful and is a waste of code.

So I though : why not the great ROL ?

W2:=ROL(W1,8)

Can it work ?

Sorry but I cannot test it so I need a quick overview at this...

 May be this could help you out

Post Entry ID:57374718

I'm not sure what your issue is with the byte/word swapping, but you may want to search for discussions about Little Endian/Big Endian formats and how to convert between the two.

Hello, 

You can develop a simple code like what Williams B told here. and put it inside a FB.

Then call this FB whenever needed in the software. 

Yes, it does function correctly.

But TIAP can be used also for S7-300/400 and maybe because of it, this topic has been stared.

William_B

SMIT SHAH

May be this could help you out

Post Entry ID: 57374718

enof

1200 (1500) has a swap instruction. If it functions correctly  then that would be the way to go?

Hi guys,

The original question was posted in the S7-300 hardware conference. What you mention does for the moment not apply here. From there also the reason why STL was mentioned.

w

Hi, 

For s7-1200 or s7-1500 you can use Slice Access :

To Swap Two bytes in a word :

W2.B0 := W1.B1

W2.B1 := W1.B0

To swap two words in a Dword :

DW2.W0 := DW1.W1

DW2.W1 : = DW1.W0

Best regards

Davinator

Hi guys,

I have to make a FC that swap the two bytes in a word to convert the hideous Siemens Word addressing to the Mankind word addressing and so I have to swap the two bytes of a word:

W1 is made by B1 and B0 so B1B0

I want that W2 is B0B1

Bit addressing is pretty painful and is a waste of code.

So I though : why not the great ROL ?

W2:=ROL(W1,8)

Can it work ?

Sorry but I cannot test it so I need a quick overview at this...

 Dear davinator

you can try using local memory its damn easy 

i have tried here i am attaching it

Smit and the others,

I started this because I needed to swap a word under tia, in scl with s7-300 and create an fc.

So even if appreciated, the tips about:

AWL, 1200,1500,FB are OTs, since for example with 1200 it is trivial this operation to swap bytes.

I have resoned and yes, with a DWORD it is not the same thing with ROR/ROL.

I posted this because if you search in internet for a method with 300 to swap the two bytes of a Word you really see some fantascentific examples that really panicked me...

That's all folks !

Little code, uses a bit more resources but with no local variables.

FernandoMx

Little code, uses a bit more resources but with no local variables.

L     #WordToSwap

L     16#00FF

AW

L     16#100

*I

T     #TempWord_0

L     #WordToSwap

L     16#FF00

AW

L     16#100

/I

T     #TempWord_1

L    #TempWord_0

L    #TempWord_1

+I

T     #WordSwapped

 Or you can use the internal function called SWAP.

STL is not even supported in the 1200 series CPU's.

FernandoMx

Little code, uses a bit more resources but with no local variables.

L     #WordToSwap

L     16#00FF

AW

L     16#100

*I

T     #TempWord_0

L     #WordToSwap

L     16#FF00

AW

L     16#100

/I

T     #TempWord_1

L    #TempWord_0

L    #TempWord_1

+I

T     #WordSwapped

What do you mean by "no local variables"? Judging by variable names there are 2 of them.

The code presented is actually an example how the STL should not be used. So, in case if there was no CAW etc. the first kind of people (because there are 10 kinds of people, you know) would come up with something like following: 

L #WordToSwap

PUSH

SLW 8

TAK

SRW 8

OW

T #WordSwapped

Xomano

I was having difficulties to do a Swap in Dword.

Note Optimized access block is required.

I think you still have those difficulties.

Your block is clearly not optimized.

And frankly saying all your difficulties are because you use non optimized blocks.

BTW, for handling byte streams there are system fcns READ_LITTLE/_BIG and WRITE_LITTLE/_BIG.