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Use only BOOL in DB (as M) or M in F and T to DB?

Created by: Per L at: 6/14/2007 10:13 AM (5 Replies)

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6/14/2007 10:13 AM	Rate (0)
Per L Posts: 29 Rating: (0)	Hi I use a DB to Scada-system If i need a flag M in the program for example Blocked, can I skip M and only use the BOOL in DB in the logic and for transfer to the Scada? I use S7-300. Whats the best thing to do??
Per L Posts: 29 Rating: (0)
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6/14/2007 11:05 AM	Rate (0)
Wizard Diamond Member Joined: 4/24/2006 Last visit: 1/9/2026 Posts: 9104 Rating: (1202)	Hi, I'm not sure I understand it right But you can use for example DB30.DBX0.0 it's the first bool in DB30. Best regards, Wizard

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6/14/2007 12:02 PM	Rate (0)
Per L Posts: 29 Rating: (0)	I can declare M0.0 as BOOL to use in my program. Set Reset And so on. Then i must copy/Transfer it´s status to DBx.DBX10.0 so Scada (HMI) Can read it. But instead of above i declare only DBx.DBX10.0 and use it in my program and HMI can also read it. Its Ok to do so or is it no good programming?
Per L Posts: 29 Rating: (0)
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6/14/2007 12:22 PM	Rate (0)
Wizard Diamond Member Joined: 4/24/2006 Last visit: 1/9/2026 Posts: 9104 Rating: (1202)	Hello, Yes, it's possible to use DBx.DBX10.0 in stead of M10.0 Best regards, Wizard

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6/15/2007 6:50 AM	Rate (1)
Aret Posts: 2348 Rating: (265)	Wizard, it's the first time i can't agree with you^) HMI (OP/SCADA) reads data asyncroniusly! So if you have programm like SET = M0.0 ...... // some code not touching M0.0 CLR =M0.0. In such case your programm may read M0.0 as 1, even though Monitor/Modify variables would show this bit as FALSE always. So it's a good way, when you make special area for HMI to read from and make only 1 write operation to this area per cycle.
Aret Posts: 2348 Rating: (265)
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6/15/2007 9:08 AM	Rate (0)
Wizard Diamond Member Joined: 4/24/2006 Last visit: 1/9/2026 Posts: 9104 Rating: (1202)	Hello Aret, You' re right , I didn't pay attention to the communication between CPU and Scada. Best regards, Wizard

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