s7300 pointer revisited

kdeadman · Mar 31, 2009

Hello, I'm working on a S7 313C cpu and i am trying to use a pointer to grab a double integer data from a DB and move that value into the first register in that DB to be used as the output register.

i am looking for a check on my code to be sure that it will be correct or at least it should be doing what i expect it should be doing as i do not have a simulator to be able to check this.

Code:

 OPN   "75K BST CHART"             // whatever DB you are using
      LAR1  P#DBX 0.0                   // Load address register 1 with a pointer into open DB
      TAR1  MD    50                    // Save address base into a DWORD for later

      L     #Curr_Idx                   // Index into the actual double integer of the DB you want
      L     4                           // If indexing Dwords, Reals, multiply by 4,
      *D                                // Curr_Idx increments by 1 for each element 
      SLD   3                           // Shift left 3 places to make offset a Pointer
      LAR1  MD    50                    // Load AR1 with the base pointer
      +AR1                              // Adds in the calculated value above to AR1
      L     D [AR1,P#0.0]               //Loads value from register in DB into accum1
      T     DBD    0                    //transfer our value into the first double of the DB called "output".

This is a function call that I pass it a double integer from 1-115 and the DB has 116 DINTs(output is first element and 2-116 are the indexed elements). so if i need element 42 from the list i pass it 42 and it will move the data from the 42nd element into the first element.

I hope this makes sense.

K

L D[AR2P#0.0] · Mar 31, 2009

The code does do as you require. Here's my implementation for comparison:

Code:

      OPN   DB     1                    // whatever DB you are using
      L     #Curr_Idx                   // Fetch Index of the actual double integer required
      SLD   5                           // Shift left 5 places for Pointer to dwords
      LAR1                              // Load AR1 with the pointer
      L     DBD [AR1,P#0.0]             // Loads value from register in DB into accum1
      T     DBD    0                    // transfer our value into the first double of the DB called "output".

kdeadman · Mar 31, 2009

Do you need to shift left 3 or 5? i must say yours is a lot more compact. Thanks for the quick reply!! much appreciated

L D[AR2P#0.0] · Mar 31, 2009

You are multiplying by 4 then shifting left 3 - this can be replaced by a shift left 5

PeterW · Mar 31, 2009

kdeadman said:
Do you need to shift left 3 or 5? i must say yours is a lot more compact. Thanks for the quick reply!! much appreciated

he shifts 5, 3 for the word/bit address and a further 2 to multiply by 4.

kdeadman · Mar 31, 2009

Makes sense.

one last thing, do we not have to point at the address register 1 to the DB to begin with? ie LAR1 P#DBX0.0 ??

thanks

L D[AR2P#0.0] · Mar 31, 2009

Using this yes:

Code:

  L     D [AR1,P#0.0]

using this no:

Code:

  L     DBD [AR1,P#0.0]

kdeadman · Mar 31, 2009

Awesome! Thanks

kdeadman · Apr 20, 2009

Multiple opening of Different DB

I have a new question.

When i use this function (FC9) to open a DB (DB4) i cannot then use a second function FC8 to open DB2 to do the same code just on a different Data Block?

Do i need to close the Shared DB before i can open a new Shared DB? and how do i do that?

Thanks
Kris

Thim · Apr 20, 2009

it depends what you want you can do alot with indirect.
Can you specify your question a little more?

kdeadman · Apr 20, 2009

What i was trying to do was with 2 different functions, open 2 different DB with them (one DB in each function) and basicaly do the same thing on both DB.

this is FC8

OPN DB 2 // whatever DB you are using
L #Curr_Idx // Fetch Index of the actual double integer required
SLD 5 // Shift left 5 places for Pointer to dwords
LAR1 // Load AR1 with the pointer
L DBD [AR1,P#0.0] // Loads value from register in DB into accum1
T DBD 0 // transfer our value into the first double of the DB called "output".

This is FC9
OPN DB 4 // whatever DB you are using
L #Curr_Idx // Fetch Index of the actual double integer required
SLD 5 // Shift left 5 places for Pointer to dwords
LAR1 // Load AR1 with the pointer
L DBD [AR1,P#0.0] // Loads value from register in DB into accum1
T DBD 0 // transfer our value into the first double of the DB called "output".

both of these functions are called within other different functions.

they do the same thing but to 2 different data charts.

when i was using this though only FC9 would work. if i changed FC8 to reference the same DB as FC9, it would work.

so Do i have to find a way of closing the DB opened in FC9 before i Open the DB in FC8?

I hope that helps

L D[AR2P#0.0] · Apr 20, 2009

You cannot close a DB, you can only open one. However, the currently open DB is saved when you call an FC, if you open a DB inside the called FC, the original DB will be opened upon returning from the called FC. Here's an example that shows what's going on:

Thim · Apr 20, 2009

I think you can define the db as a "in" of type integer
Then in the FC you say

L iDbNumber
T Temp.something // this is of the type Word

Opn DB[Temp.something]

So no you give the number of the DB you want to work with in the FC when you call the FC

cjd1965 · Apr 21, 2009

Code:

      OPN   DB     1                    // whatever DB you are using
      L     #Curr_Idx                   // Fetch Index of the actual double integer required
      SLD   5                           // Shift left 5 places for Pointer to dwords
      LAR1                              // Load AR1 with the pointer
      L     DBD [AR1,P#0.0]             // Loads value from register in DB into accum1
      T     DBD    0                    // transfer our value into the first double of the DB called "output".

Hi Is there any reason why the final move (T DBD 0 ) could not be moved to the block output directly? I realise the OP wanted it to be posted into the first dword of the datablock.

I am considering using spmthing like this but with a struct of 3 dwords for each lookup.

Cheers

L D[AR2P#0.0] · Apr 21, 2009

Not sure what you mean - can you give a specific example ?

s7300 pointer revisited

kdeadman

Member

L D[AR2P#0.0]

Lifetime Supporting Member

kdeadman

Member

L D[AR2P#0.0]

Lifetime Supporting Member

PeterW

Member

kdeadman

Member

L D[AR2P#0.0]

Lifetime Supporting Member

kdeadman

Member

kdeadman

Member

Thim

Member

kdeadman

Member

L D[AR2P#0.0]

Lifetime Supporting Member

Thim

Member

cjd1965

Lifetime Supporting Member

L D[AR2P#0.0]

Lifetime Supporting Member

Similar Topics