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Step 7 SCL help with increasing/decreasing variable

Created by: lakotnik at: 6/21/2013 11:20 AM (6 Replies)

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6/21/2013 11:20 AM	Rate (0)
lakotnik Posts: 22 Rating: (0)	Hello i have problem with my code and i don't know how to fix it. When i press "dvigovanje" it increases "stanje" and when i press "spuscanje" nothing happens ("stanje" should decrease ). Can someone tell me what am i doing wrong? Regards [code][/code] VAR_INPUT dvigovanje: BOOL; spuscanje:BOOL; END_VAR VAR_TEMP stanje:DINT; zgornja_vrednost:DINT; spodnja_vrednost:DINT; vrednost:DINT; delec_kota:REAL; temp_real:REAL; END_VAR VAR_OUTPUT trenutni_kot:REAL; END_VAR zgornja_vrednost:= DINT#27; spodnja_vrednost:= DINT#0; vrednost:= DINT#1; delec_kota:= 180.0/27.0; IF dvigovanje = true THEN IF stanje <= zgornja_vrednost THEN stanje := stanje + DINT#1; //new ELSIF stanje > zgornja_vrednost then stanje := zgornja_vrednost; // END_IF; END_IF; IF spuscanje = true THEN IF stanje >= spodnja_vrednost then stanje := stanje - DINT#1; ELSIF stanje < spodnja_vrednost THEN stanje := spodnja_vrednost; END_IF; END_IF; temp_real := DINT_TO_REAL(stanje); trenutni_kot:= temp_real * delec_kota; END_FUNCTION_BLOCK [code][/code]
lakotnik Posts: 22 Rating: (0)
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6/21/2013 4:15 PM	Rate (0)
0_Einstein Grandmaster Joined: 7/7/2010 Last visit: 1/12/2026 Posts: 16358 Rating: (2522)	As I read it, the function block is using temp tags without first initializing them. I believe temps are unpredictable if used without first assigning them a value. If you meant for your first temp to be assigned a known value before comparing it, your block might do as you expect.
	science guy
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6/21/2013 5:39 PM	Rate (0)
yy1 Posts: 535 Rating: (112)	Dear lakotnik, the variable, which is mentioned by huggy_d1 is "stanje" Best regards, yy1
yy1 Posts: 535 Rating: (112)
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6/21/2013 6:40 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 1/8/2026 Posts: 1561 Rating: (540)	You are expecting TEMP variables (in this case stanje) to hold their last set/used value between scans. TEMP variables will not do this as they are stored on the stack and as their name suggests, they are temporary and only exist whilst the block is running. They are destroyed when the block exits and recreated again when the block next runs. For the code to work as you expect, stanje must be part of the static data for the block and as such it has to be declared in the VAR section. Static data variables are held in the instance DB, hence why they can retain their values between scans. So the rule is:- Any variable that you setup and use just for the duration of the block scan can be a TEMP variable or a VAR (static) variable. Any variable that you want to have a "permanent" memory that persists between scans, then it has to be a static variable and declared in the VAR section.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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6/21/2013 6:41 PM	Rate (0)
0_Einstein Grandmaster Joined: 7/7/2010 Last visit: 1/12/2026 Posts: 16358 Rating: (2522)	I think if youmake stanje a static tag with initial value of 0, it should work fine as is.
	Last edited by: huggy_d1 at: 6/21/2013 6:43 PM smiffy Last edited by: huggy_d1 at: 6/21/2013 6:42 PM [what smitty said... he beat me to it] science guy
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6/21/2013 6:41 PM	Rate (0)
lakotnik Posts: 22 Rating: (0)	Thank you very much
lakotnik Posts: 22 Rating: (0)
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8/30/2017 3:36 PM	Rate (0)
Wit_Moderator Moderator Joined: 8/21/2014 Last visit: 12/19/2025 Posts: 1098 Rating: (15)	New question published by ToFast is split to a separate thread with the subject Its possible to declare in FC the static variable. Best regards The Helping Hand
	My Forum is the place to personalize your profile, track your topics, and maintain content that interests you. Best regards Wit_Moderator
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