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NEGATIVE OFFSET IN INDIRECT ADDRESSING

Created by: joisramesh at: 7/1/2011 12:46 PM (3 Replies)

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7/1/2011 12:46 PM	Rate (0)
joisramesh Posts: 40 Rating: (1)	Hi All, I want to decrement the offset used in indirect addressing. For example, L 120 SLW 3 LAR1 OPN "HMI_GLOBAL_DATA" L #T_ENA_COUNT ENAA: T #T_LOOP_COUNT S DBX [AR1,P#0.0] +AR1 P#0.1 LOOP ENAA here in the last line I want to decrement the AR1 by P#0.1 every time it loops. So please share the ideas of implementing this. Regards, Ramesh Jois.
joisramesh Posts: 40 Rating: (1)	Last edited by: joisramesh at: 7/1/2011 12:47 PM
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7/2/2011 7:23 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 9/5/2025 Posts: 5112 Rating: (768)	You're out of luck. Nor negtive offsets nor decrementing ARs are possible.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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7/2/2011 8:46 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 8/31/2025 Posts: 6874 Rating: (1368)	Hi You are lucky, because there is a way to implement so Indirect addressing by AR1 fritz While I personally also miss a "-AR1" and "-AR2" command in S7,there is a relativelyeasy way around it as shown below (this is what I typically do anyhow and is also what jklmsuggested): L-32// need to subtract 32 Bits (= 1 REAL) +AR1 // from AR1 (and wish S7 had a "-AR1 P#x.y" command) And you are a super lucky because you can check one application in this link: [code] L #ein T #ein1 L P##ein1 LAR1 LAR2 L P#1.7 +AR2 L 8 llp: T #loop_count A [AR1,P#0.0] = #temp1 A [AR2,P#0.0] = #temp2 A #temp2 = [AR1,P#0.0] A #temp1 = [AR2,P#0.0] L P#0.1 +AR1 L -1 +AR2 L #loop_count LOOP llp L #ein1 T #aus[/code] Regards
	Last edited by: hdhosseini at: 7/2/2011 8:55 PM Demo Channel on Youtube
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7/6/2011 11:37 AM	Rate (0)
Aret Posts: 2348 Rating: (265)	Well, if we see problem in details its actually quite simple^) P#x.y is just DWORD, where contents = x*8+y. Next - pointer can contain area type and look like P#DBXx.y. In this case it is represented as P#x.y + addon in most-significant byte (84 in case of DBX). So in both cases to subtract pointer you can use rule as if it was ordinary DINT. The only thing you should care in this case is not crossing 0, because if you cross it you will get wrong AREA type in pointer, so result would be unpredictable.
Aret Posts: 2348 Rating: (265)
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