S5 to S7 "DO" translation question..

uptown47 · Oct 12, 2011

Hi all,

When the 'automatic' S5 to S7 translates comes across a DO instruction it translates it but I have a question about the translation.

Could you tell me if I'm right here:

Code:

S5 CODE IS:
DO FW 240
C DB 0

I understand what this code is doing. It's taking the value of FW 240 and calling the corresponding Datablock (i.e. if FW 240 = 40 then its calling DB 40).

This is the S7 Conversion:

Code:

(#conv_akku1 = TEMP Dword
#conv_index = TEMP Word)
 
T #conv_akku1
L MB 241
T #conv_index
TAK
L #conv_akku1
OPN DB[#conv_index]

This is the same code again with my comments next to it for what I think is going on with the Accumulators etc...

Code:

T #conv_akku1       // Transfer the contents of Accumulator
                    // 1 into #conv_akku1 ?? WHY ??
 
L MB 241            // Load value of MB241 into Accumulator 1
                    // - old Accu 1 value moved to Accu 2
 
T #conv_index       // Transfer Accu 1 (value of MB241) into
                    // #conv_index
 
TAK                 // Swap contents of Accumulator 1 and 2 so
                    // now Accumulator 1 = whatever was in
                    // Accu 2 (Instruction pointer perhaps?)
                    // as all this code takes place in a FB.
                    // Accu 2 is now equal to value of MB241
 
L #conv_akku1       // Accu 1 now equal to #conv_akku1
                    // Accu 2 now got its instruction pointer?
                    // back 
 
OPN DB[#conv_index] // Open DB of value MB241

Am I right with this or am I off on a tangent here?

It seems like an awfully complicated way of doing a "DO" instruction? Is there no simpler way ??

Many thanks for any help / reassurance you can give me.

Cheers

uptown (John) ;-))

TurpoUrpo · Oct 12, 2011

Remember the magic word, its automatic translator. It has to take into account that maybe there was data that will be used after opn in accus.

Im sure you can yourself find many ways to do it simpler

uptown47 · Oct 12, 2011

Hi TU,

I did wonder why I couldn't just have:

Code:

OPN DB[MW 240]

?

What about my interpretation of the accumulators?? Am I on the right track or way off??

Thanks for your (very) prompt help

;-)

L D[AR2P#0.0] · Oct 12, 2011

In Step5 you could only open data blocks up to DB255. The DB number is in MB241 and MB240 may contain some data which would not be used by the DO instruction, so to replicate the functionality in Step7, MB241 has to pass through the accumulator to get written to the temp variable for the indirect opening of the DB - this would have corrupted the accumulator so the accumulator is first copied to a temp for storage, MB241 can then be loaded to Accu 1 and stored in the temp used for the indirect opening of the DB. Accu1 and Accu2 are restored to their previous state and then the DB is opened.

If you know that MW240 contains the DB number then your coding is correct.

Jeebs · Oct 12, 2011

L D[AR2 said:
Accu1 and Accu2 are restored to their previous state and then the DB is opened.

Is it just me or isn't there a TAK missing right before the Load to completely restore ACCU1 and ACCU2 to what they were before the datablock is opened?
According to me, ACCU1 and ACCU2 will now have the same value, that of #conv_akku1.

If I'm mistaken......well erm......whoops?

L D[AR2P#0.0] · Oct 12, 2011

No you are not mistaken - in my Berger there is a conv_accum2 used in the example DO conversion.

Here's confirmation of Uptown's code executing:

uptown47 · Oct 13, 2011

L D[AR2 said:
In Step5 you could only open data blocks up to DB255. The DB number is in MB241 and MB240 may contain some data which would not be used by the DO instruction, so to replicate the functionality in Step7, MB241 has to pass through the accumulator to get written to the temp variable for the indirect opening of the DB - this would have corrupted the accumulator so the accumulator is first copied to a temp for storage, MB241 can then be loaded to Accu 1 and stored in the temp used for the indirect opening of the DB. Accu1 and Accu2 are restored to their previous state and then the DB is opened.

If you know that MW240 contains the DB number then your coding is correct.

Thanks for the explanation re. Datablocks up to 255 et al.

Are my comments correct for how I interpreted the code?

And, reference Jeebs point, is this code incorrect then? This is the code that the 'auto' translator came up with?

Thanks again for all the help

;-)

S5 to S7 "DO" translation question..

uptown47

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TurpoUrpo

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uptown47

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L D[AR2P#0.0]

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Jeebs

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L D[AR2P#0.0]

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uptown47

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