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datablock greater than 4096byte (max limit is 64Kb). How can variables be accessed with indirect register addressing with this stringent limit?

Created by: Giuliano69 at: 12/2/2011 12:33 AM (6 Replies)

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12/2/2011 12:33 AM	Rate (0)
Giuliano69 Posts: 21 Rating: (0)	Hi fritz, the P#4096.0 limit, prevents from ADDING to ARx address a value greater than 4096. But what about datablock greater than 4096byte (max limit is 64Kb). How can variables be accessed with indirect register addressing with this stringent limit? As an example I have a huge DB (256 array of 16 real + 256 array of 16 int+...), that suprasses the 4096 limit of P# pointer addressing. How to deal with such situations ? How to forge the pointers in function for indirect addressing? Should LAR2 be capable or fail to load the 34816 pointer value ? In which other way is it possible to reach such a "far" address ? OPN DI 3 // STORE DB L L#34816 // offset inside DB to be read SLW 3 // pointer shift conversion LAR2 // address loading L DIW [AR2,P#0.0] //load index from STORE at pos 34816 T #HistPos //save index locally
Giuliano69 Posts: 21 Rating: (0)	Last edited by: O_Moderator at: 12/2/2011 9:54 AM new subject after splitting from /tf/WW/en/Posts/54236#top
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12/2/2011 4:53 AM	Rate (1)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 9/23/2023 Posts: 2987 Rating: (1034)	Hello Giuliano69 I fear there is a bit of a misunderstanding,so let me start by clarifying a few things first: What you need to be mindful of is the amount of offset you can add via the +AR1 or +AR2 commands. These only take accu 1 low into account and as such have a limitof4096 bytes (to be precise 4095.7 is the highest number you can add via the +AR1 or +AR2 command). In fact, if you use "+AR1 P#x.y" as a one line command, the editor won't allow you to use aan "x.y" value that exceeds "4095.7" If you however do"L P#x.y" "+AR1" with values between4096.0 and 8192.0 you will in fact subtract from AR1 as below: "L P#4096.0" "+AR1" subtracts 4096 bytes fromAR1 "L P#4097.0" "+AR1" subtracts 4095 bytes from AR1 "L P#8191.0" "+AR1"subtracts one byte from AR1 "L P#8192.0" "+AR1" is a zero sum game. "L P#8193.0" "+AR1" adds one byte toAR1 While the above seems"nasty",this behaviour can be "exploited" to subtract from AR 1 (since there is no "-AR 1" command). Anyway, attached is a screendump with some comments which shall help in making sense out of the above. As for your logic: L L#34816 // offset inside DB to be read SLW 3 // pointer shift conversion LAR2 // address loading change the "SLW3" to a "SLD 3" and it will be ok. Twolast (important) things: 1.) AR2 is used by FB's to hold the multi instance offset adress and you must be very careful when using AR2 in an FB (ideally avoid AR2 all together in a FB) 2.) If you want your FB to be multi instance capable you must take the AR2 based multi instance offset adressinto account. Have a look at the FAQ collection below for more on this: STEP 7 -- Creating S7 programs -- Indirect Addressing I hope this helps Attachment AR Games.jpg (81 Downloads)
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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12/2/2011 11:55 AM	Rate (0)
Giuliano69 Posts: 21 Rating: (0)	Thanks Fritz for your explanation of the +AR1 adding only the low word of ACC1 I understand the LAR1 load the whole ACCU1 register. It find clear the two's complement in case of 4096 [code]4096 #2#000 1000000000000 NOT #2#111 0111111111111 0111111111111 = 4095[/code] I find difficult in inderstanding the other exaplesmath pointer examples. The number should be interpreted as two's complement and subtracted So: [code] L L#8191 +AR1[/code] [code]8191 #2#000 1111111111111 NOT #2#111 0000000000000[/code] Should the +AR1 instruction add 0 ? (ADD LOW ACCu1 register) Why +AR1 add 1 in your example [code]L#34816 L L#34816 (L W#2#100 0100000000000) SLW 3 ( W#2#010 0000000000000) LAR1[/code] Shifting 3left, should the LOAD AR1 reguster take both the LOW and §HIGH ACCU1 words (16384)? Why 2048 ?
Giuliano69 Posts: 21 Rating: (0)
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12/2/2011 12:33 PM	Rate (0)
Giuliano69 Posts: 21 Rating: (0)	One more consideration on the general approach with HUGE data block. Considering that the values CANT be complitely indirected addressed with pointer addiction (4096 limit), but only with ARx loading, is it deprecated to use DB larger than 4Kb ? Are there any other/suggested way to deal with huge DB accessing ? If I split the huge DB in smaller DBs, i could access sequentially the DB ( OPN DI 1,2,3,...), is it correct that the AR2 register content is not affected by OPN DI changes, letting to point sequentially the same "local" address in DBn, DBn+1,.... without math pointer with AR2 ?
Giuliano69 Posts: 21 Rating: (0)
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12/2/2011 6:01 PM	Rate (0)
Marciano Bronze Member Joined: 4/30/2007 Last visit: 3/9/2023 Posts: 231 Rating: (23)	Giuliano69 I find difficult in inderstanding the other exaplesmath pointer examples. The number should be interpreted as two's complement and subtracted So: L L#8191 +AR1 8191 #2#000 1111111111111 NOT #2#111 0000000000000 Should the +AR1 instruction add 0 ? (ADD LOW ACCu1 register) Why +AR1 add 1 in your example You did One's complement above, for Two's complement it is missing adding +1 Giuliano69 L#34816 L L#34816 (L W#2#100 0100000000000) SLW 3 ( W#2#010 0000000000000) LAR1 Shifting 3left, should the LOAD AR1 reguster take both the LOW and §HIGH ACCU1 words (16384)? Why 2048 ? The addressing in pointers go to bit level (Byte.Bit) and takes three bytes for that, because this it is needed use the shift SLD instead SLW.

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12/2/2011 8:41 PM	Rate (0)
Marciano Bronze Member Joined: 4/30/2007 Last visit: 3/9/2023 Posts: 231 Rating: (23)	Giuliano69 One more consideration on the general approach with HUGE data block. Considering that the values CANT be complitely indirected addressed with pointer addiction (4096 limit), but only with ARx loading, is it deprecated to use DB larger than 4Kb ? Are there any other/suggested way to deal with huge DB accessing ? Dear Giuliano69 In previous post Fritz has well illustrated how AR1 works. And what he refers as limited is the offset adding, not the indirect addressing itself. I am sending one example of accessing a 64K Datablock using indirect addressing and offsetting AR1. Regards, Marciano Attachment HugeDB.JPG (80 Downloads)

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This contribution was helpful to 1 thankful Users fritz

12/2/2011 8:44 PM	Rate (0)
Marciano Bronze Member Joined: 4/30/2007 Last visit: 3/9/2023 Posts: 231 Rating: (23)	Here the S7 file ... P.S.:Does someone knows if is possible upload more than one file? Attachment Hugedb.zip (42 Downloads)

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