Hi Experts,

I'd like to know the real purpose of indirect addressing. Where it is indispensable to use them? What advantage do I gain using them instead of using direct addressing. 

Other than that, I didn't understand very well what does : "Indirect addressing offers the option of addressing operands whose address is not calculated until during runtime" mean. 

In case you need, I use TIA v12 on 300 series CPU with SCL.

Thank you in advance,

Janko

jankoslayer

Hi Experts,

I'd like to know the real purpose of indirect addressing. Where it is indispensable to use them? What advantage do I gain using them instead of using direct addressing. 

Other than that, I didn't understand very well what does : "Indirect addressing offers the option of addressing operands whose address is not calculated until during runtime" mean. 

In case you need, I use TIA v12 on 300 series CPU with SCL.

Thank you in advance,

Janko

 Hello,

Using indirect addressing save us writing iterative tasks much easier with less  memory cost.About calculating addresses in runtime, it is critical for STL with absolute addresses are calculated by indirect addressing syntax and too many error may happen if calculation and design is not done with care.In SCL, normally this problems are minimized while you are mainly working with symbolic addresses (dominantly) .

I hope these comments  help,

hdhosseini

Thank you for replaying Mr,

I had the same impression that the use of Indirect Addressing is related to better memory management (but now I have the confirmation ). The problem I have is the next one: do i really need to declare some variable at %DB100.DBX12.5 for example before using indirect addressing or it will be done during runtime?! 

#Var_Bool:= %DB100.DBX12.5;

Janko

jankoslayer

Thank you for replaying Mr,

I had the same impression that the use of Indirect Addressing is related to better memory management (but now I have the confirmation ). However could you be more precise about runtime calulation, in particular if you could give me an example of variables of which memory is calculated before runtime as well as an example of variables of which memory is calculated during runtime. 

Janko

 MB0 is memory area known before execution while in the following code section, you have no idea what would be the memory area you are requesting to read:

L  MW100

SLD  3

LAR1

L  MB[AR1,P#2.0]

T QB0

I reformulated the previous the answer on your reply. Sorry for inconvenience.

Janko

unknown user

The problem I have is the next one: do i really need to declare some variable at %DB100.DBX12.5 for example before using indirect addressing or it will be done during runtime?! 

#Var_Bool:= %DB100.DBX12.5;

 You don't need an intermediate address.Normally, you need loops and loop counter variables such as i,j. To perform indirect addressing in SCL , you 2 options:

-Using arrays and access elements in array just by calling name of array and a int parameter like i as loop counter.Check the following example:

ORGANIZATION_BLOCK OB1
author:hdh

VAR_TEMP
// Reserved
info : ARRAY[0..19] OF BYTE;
// Temporary Variables
i:INT;
j:INT;
END_VAR

// Statement


FOR i:= 1 TO 10 BY 1 DO
// Statement Section

FOR j:= 1 TO 10 BY 1 DO

test.hd[i,j]:=i*j;

;
END_FOR;
;
END_FOR;


;
END_ORGANIZATION_BLOCK

Q[i,j] that i is the byte index and j is the bit index

DB10.DX[i,j]

Hello,

Perhaps the following topic might help:

Siemens S7 Indirect Addressing

jankoslayer

So I'd say that this becomes something similar to using standard pointers,C like  except that I  (always) have knowledge of all variables, event of the pointer?

 In SCL, you are right and it is similar.The exception comes from different memory concept and their limitation we encounter in PLCs.

hdhosseini

 In SCL, you are right and it is similar.The exception comes from different memory concept and their limitation we encounter in PLCs.

 That's it!!! I wanted to hear that! Thank you so much!