2/26/2015 8:20 PM | |
Joined: 9/27/2006 Last visit: 9/22/2024 Posts: 12282 Rating: (2685) |
Hello gerard; When you speak of TON, it seems you are refering to SFB4, from the IEC functions Library. An SFB is a standard FB, and every FB (function block) you use in your programs will require an instance datablock, so that values required for the function block are retained. For example, when you use a timer function (such as TON), you want to input a preset value, and hjave access to the timer remaining value. These are available as STAT variables in your IDB, and can be accessed by the program even when the FB is not being called by your program. To simplify things, you could have a look at the following discussion (from a long time ago, it seems): Difference between FB and FC's Or simply open the basic manual Programming with Step 7, where you will find this extract:
4.2.3.3 Function Blocks (FB)
Function blocks (FBs) belong to the blocks that you program yourself. A function block is a block "with memory." It is assigned a data block as its memory (instance data block). The parameters that are transferred to the FB and the static variables are saved in the instance DB. Temporary variables are saved in the local data stack.
Data saved in the instance DB are not lost when execution of the FB is complete. Data saved in the local data stack are, however, lost when execution of the FB is completed.
Hope this helps, Daniel Chartier
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