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Step7 Instance Data block (IDB) STAT memory WinCCflexible access practice

Created by: Floyd at: 2/1/2008 12:41 AM (4 Replies)

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2/1/2008 12:41 AM	Rate (0)
Floyd Posts: 130 Rating: (1)	All: Looking for advice here. Is it bad practice to access STAT memory of a Instance Data Block directly from WinCC/WinCCflexible or from elsewhere in a simatic project? Example: I have object A that has several setpoints set from the HMI. It is easiest to directly write these setpoints from the HMI to the STAT memory of the object. Is this bad practice? The alternate method would be to send it to the Object as an INPUT. Thanks for any input. If it makes any difference, we program in LADDER not STL, and asthetics of the program may be different. Thanks
Floyd Posts: 130 Rating: (1)
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2/4/2008 7:51 PM	Rate (0)
bunglehead Posts: 54 Rating: (3)	It's a bad practice in meaning of program modeling and structuring, cause the purpose of an instance db (and FB in general) is to encapsulate the internal state, structure and give just only a pure interface of FB. But S7-300/400 doesn't offer any memory protection or access control (I mean that there's no definition of variable scope), so you can choose to use IDB if for example interface rewriting is not possible during work at plant that supposed to be finished today-tomorrow.
bunglehead Posts: 54 Rating: (3)
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2/6/2008 12:33 AM	Rate (0)
Floyd Posts: 130 Rating: (1)	Any advice on FB designs that have a lot of Parameters In and Out or am i trying to represent to large a process within a block? My example would be a machine that has perhaps: 8 process inputs 8 process outputs 8 alarm setpoints 8 status outputs 8 alarm outputs That turns into a block with 16 inputs and24 outputs for example, i could access a lot of the internal data directly at the IDB level that is really only significant for indication verses the running process. Is using a FB to represent a machine pushing the limits or does it just look ODD because i view the block in LAD verses STL
Floyd Posts: 130 Rating: (1)
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6/19/2009 8:58 AM	Rate (0)
Import-User-1 Gold Member Joined: 8/10/2005 Last visit: 2/7/2022 Posts: 3609 Rating: (28)	Import of a Technical Question of an User Plectrotionwrote: HI I also have same question. I have multiple Instance DB with instance of diffrent Valves & Agitators. Q1. Can we directly link instance db memory location for Input/Output parameters from HMI / other program in the PLC. I have planned to create another Shared DB for each Instance DB.This Shared DB variables will be used for Calling multiple Instance FB for Valve/Agitator.Then Actual analog Input/Output/Di/DO will be passed to Shared DB.HMI will be using this shared DB for HMI-PLC interfacing.---It is very odd to me, I think I am using Double memory location for each variables. Please help me, I have to start assigning parameters once I get right procedure. Thanks

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6/19/2009 9:49 AM	Rate (0)
fritz Diamond Member Joined: 10/7/2005 Last visit: 2/9/2023 Posts: 2955 Rating: (1019)	Hello floyd have a look at this recent thread which has all the advise and opnions that you need. Cheers Fritz
	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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