How can write/read a string using peek or poke instruction?

huggy_d1

Attached is a simple call to the following SCL FBs to first find the index, and then lookup the reference value from the index.

You will want to use internal error handling within these FBs (see other forum examples and the F1-help on how to implement this).  Internal error handling will allow you to not worry so much about accidentally changing the size of your array and suddenly the bounds change in such a way that one of these FBs fail and cause a PLC fault......  You have been warned.

These are ready to import as external SCL files. The DB is set up virtually identically.  The UDT was named RECIPE_UDT.

FUNCTION_BLOCK "FIND_REF_INDEX"
{ S7_Optimized_Access := 'FALSE' }
VERSION : 0.1
VAR_INPUT
  REF : UInt;
  dbNum : DInt;
  LIST_LOW_BOUNDS : Int;
  LIST_UP_BOUNDS : Int;
END_VAR

VAR_OUTPUT
  INDEX : UInt;
  ERR : Bool;
END_VAR

VAR_TEMP
  i : Int;
  SAVE_OFFSET : Int;
END_VAR

VAR CONSTANT
  UDT_OFFSET_TO_REF : Int := 2;   // # bytes into UDT we find the "reference" sub-component of the UDT
END_VAR

BEGIN
// error check bounds inputs
IF (#LIST_LOW_BOUNDS < #LIST_UP_BOUNDS) THEN
  #ERR := false;
  //
  // NOTE: IF YOU WANT BULLET-PROOF CODE, HANDLE ERRORS INTERNALLY AND EXIT IF BOUNDS CHECK FAIL DURING LOOPING
  //
  FOR #i := #LIST_LOW_BOUNDS TO #LIST_UP_BOUNDS DO
     // loop through until we locate the input REF value.  Save that index number and return it (#i).
     #SAVE_OFFSET := PEEK(area := 16#84,
                          dbNumber := #dbNum,
                          byteOffset := #i * #UDT_OFFSET_TO_REF);
    // check to see if this recipe contains the referenced input REF value
    // if so, return the index into the recipe array it is found, and stop looking
    IF (#SAVE_OFFSET = #REF) THEN
      #INDEX := INT_TO_UINT(#i);
      RETURN;
    END_IF;

  END_FOR;
ELSE
  #ERR := true; // some error occurred
END_IF;

END_FUNCTION_BLOCK

 

FUNCTION_BLOCK "FIND_NEXT_VALUE"
{ S7_Optimized_Access := 'TRUE' }
VERSION : 0.1
VAR_INPUT
  INDEX : UInt;
END_VAR

VAR_OUTPUT
  VALUE : UInt;
  ERR : Bool;
END_VAR

VAR_TEMP
  i : Int;
END_VAR

BEGIN
// IF the FB exits before the end, ERR will be true
#ERR := true;
// compute next array index
#i := UINT_TO_INT(#INDEX) + 1;
// look up value from array
#VALUE := "Data_block_2".Recipe[#i].value;
// if all good, no error
#ERR := false;
END_FUNCTION_BLOCK 

hi

could you say how can i write/read a string using peek or poke instruction

Provided:

plc is 1214

tia v15

------------------------------------------------------------------------------------------
Split from indirect addressing 1200.

Hello Rakeysh,

see the following informations of the FAQs in the network:

How do you address securely and indirectly in STEP 7 (TIA Portal)?
https://support.industry.siemens.com/cs/ww/en/view/97552147

In STEP 7 (TIA Portal), how can you implement indirect addressing in an SCL program?
https://support.industry.siemens.com/cs/ww/en/view/59623719

How in STEP 7 (TIA Portal) V11 do you program the data type "VARIANT" for indirect addressing for the S7-1200/S7-1500?
https://support.industry.siemens.com/cs/ww/en/view/42603286

Thank you for the Reply Cicero

But what i am looking for is not present in the 3 links 

just i need to write a data in a DB after a process in the function call 

and the data to be written into DB  can be of  any kind, Of Course the DB is prepared with the data types filled

It is a Very Very Big Problem with siemens PLC 

in MITSUBISHI PLC you can write any type data into registers

and in that if i move hexadecimal 41 it will consider it as ASCII "A"

but here in siemens it is quite difficult

i have tried the same logic in siemens it is moved and i am working on that  i think i could acheive that 

mean while i could request you all to give a simple solution to this

here the plc is 1214 not 300/400/1500

Hello.

Please review the attach picture.
Is it of any value to you?

Additionally -
To be able to use the POKE function, the code should be in SCL and the DB to be manipulated should be not-optimized. The DB attribute is seen below:

BR

HI #dp

i have already made the db free from optimized without that i cannot guess the offset

yes i know the first and last words of string cannot be disturbed(system used)

its some what new trick you are using, let me try this

Thank you 

Hello.

Rakeysh

yes i know the first and last words of string cannot be disturbed(system used)

Please allow a correction.

The STRING uses only the 1st WORD for system related functions. Byte 0 is the capacity and Byte 1 is the space already used (length). These are USINT values.

A STRING is not the same as an array of CHAR. Some brands use these as the same, but Siemens do not. This is important to note when linking to non-Siemens devices like HMIs.

Defining a tag as STRING[20] means there is a capacity to store 20 ASCII characters. That is 20 BYTEs of contents. With the header, the tag has a footprint of 22 BYTEs in this case.

"DX".modify[#index]  will be able to read-write all the contents characters, where #index can be a value between 1 and 20. Index positions [-1] and [0] cannot be accessed in this way. There is a string instruction that can read the occupied length (#index = 0).

Other powerful interrogation and manipulation instructions are available that is worth investigation.

Finally .. careful for using plainly STRING as a datatype. This makes the storage to be able to take the maximum character capacity which steals very much data spaces.

BR

My problem is resolved i used stat and for loop

[snip]

Hello Rakeysh 

you can use these instruction it's worded for me

Hi, do you know what is the ascii character that make end of the string?

Im doing a POKE read for a STRING[16]= 'This is a test' , I start reading after byte 2, and what i got in observation value is 'This is a Test$0'.

For what i read $ is a special character that canot be showed as observation value and is represented as '$".

So i want to know what char is that to find it and delete it from my string

Thanks in Advance

#dP

Hello.

Rakeysh

yes i know the first and last words of string cannot be disturbed(system used)

Please allow a correction.

The STRING uses only the 1st WORD for system related functions. Byte 0 is the capacity and Byte 1 is the space already used (length). These are USINT values.

A STRING is not the same as an array of CHAR. Some brands use these as the same, but Siemens do not. This is important to note when linking to non-Siemens devices like HMIs.

Defining a tag as STRING[20] means there is a capacity to store 20 ASCII characters. That is 20 BYTEs of contents. With the header, the tag has a footprint of 22 BYTEs in this case.

"DX".modify[#index]  will be able to read-write all the contents characters, where #index can be a value between 1 and 20. Index positions [-1] and [0] cannot be accessed in this way. There is a string instruction that can read the occupied length (#index = 0).

Other powerful interrogation and manipulation instructions are available that is worth investigation.

Finally .. careful for using plainly STRING as a datatype. This makes the storage to be able to take the maximum character capacity which steals very much data spaces.

BR