Tough question of Siemens programming

Hi,

I'm wondering how to program a function that has an integer(or word) input but return the value contains in the address of the input.

for example, I have a RTD with address of 512, my function gets the input of 512 and gives back the temperature of PIW512.

----------------------
Function getRTD: int;
Var_Input
Addr:int;
end_Var

getRTD:=???????;
End_function
-----------------------

It would be fine if the program is written in LAD or STL. But if you know how, please also tell me how to return a digital I/O's value (probably in byte or word). Thanks!

Best Regards

in the block create 4 TEMP's

PerPointer Type = DWORD .. Pointer
IntVal Type = WORD .. Temp location for value in PIW
Ret_Stat Type = WORD .. For return status of scale
Read_Val Type = REAL .. For read value




Use Intval as input for SCF105, would also need inputs for max and min values

In SCL:

PeterW said:

in the block create 4 TEMP's

PerPointer Type = DWORD .. Pointer
IntVal Type = WORD .. Temp location for value in PIW
Ret_Stat Type = WORD .. For return status of scale
Read_Val Type = REAL .. For read value

Code:

L #Addr
SLD 3
T #PerPointer
 
L PIW[#PerPointer]
T #IntVal
 
Call SFC105

Use Intval as input for SCF105, would also need inputs for max and min values

Click to expand...

L D[AR2 said:

In SCL:

Code:

FUNCTION getRTD : INT
VAR_INPUT
    Addr:INT;
END_VAR
getRTD := WORD_TO_INT(PIW[Addr]);
END_FUNCTION

Click to expand...

Thank you very much for your help. I had a few days off so I didn't try those methods and response.

I got that SFC105 is the system funtion for the address-value conversion from Peter, but SCL seems much easier to me, so i tried it today and it works well on PIW, IW and QW.

L D[AR2,P#0.0], Can you show me how to get the value of PQW? My SCL can only do
PIW[Addr]:=WordVar;
but not
WordVar:=PIW[Addr];

Thank you guys again!

You cannot read a PQW value.

Got it. Thank you!

Once came across something like this below.
Indirect adressing of IO points. It confused the s..t out of me as the IO used that way didn't show up in the x-ref



L #LSL_Addr_Byte
SLD 3
L #LSL_Addr_Bit
+D
LAR2
A I [AR2,P#0.0]
....

??????

A function can't possibly know the address of the variable passed to it. The examples you show will return the address of the passed variable on the stack but not where is actually is.

Thank you for discussing this question.

I read some documents, and I understand the point of HenkieD's program. The one by my hand, called Pointers and Indirect Addressing in S7 PLCs, says that an area pointers is a 32bits struct which include 8 bit type bits, and byte address bits, and 3 bit address bits.

for example, P# M12.3 = 10000011 00000000 00000000 01100011

Therefor, that program loads an address, shift left for 3 bits, then add the bit address (3 bits). AND IT SHOULD ADD THE AREA TYPE BITS (first 8 bits), then form an address pointer.

I am not sure if the instruction A I [AR2,P#0.0] is to read the Analog input of the pointer, but that is how it works.

Anyway, i tried with SCL to read the area pointer of PIW512, but failed. I don't know if area point is only for STL, but since I can use PIW directly in SCL, i stopped working on it.