Sunday, January 30, 2011

Data Block and Timer Functions of Simatic S7





Data blocks are global memory areas of a size by the user in each case. They are addressed by a block number data. Data blocks are required to exchange data via interfaces with external devices such as for instance, the NCK or operator interfaces.

In contrast to data blocks in the Simatic S7 environment which are loaded from programming device/PC or generated in the program, the memory area for such blocks must always be allocated by the user in the development and test environment on the PC. The CS7DLIB sets up automatically the data blocks used as standard in the SINUMERIK 840D.

It can be opened once a data block exists. The appropriate function call OPN_DB() supplies a “handle” in exchange which is required for all further calls of the data block. You can have several data blocks opened at the same time and access them optionally via the functions below if you are managing and using the appropriate handles.

Simatic S7 offers the programmer 5 different types of timer, each type with its own characteristics:
• The pulse timer is set to the specified value by a positive edge at logic input. This value is counted down to 0 in specified clock cycle.
• The timer with extended pulse is set to the specified value by a positive edge at logic input r/o. this value to counted down to 0 in the specified dock cycle. The logic output remains at 1 as long as the timer value is higher than 0.
• The timer with ON delay is set to the specified value by a positive edge at logic input r/o. this value is counted down to 0 in the specified clock cycle. The logic output does not, however, switch to 1 until the time has expired and input r/o is still at 1.
• The timer with OFF delay is set to the specified value by a negative edge at logic input r/o.
• The timer with latched ON delay is set to the specified value by a positive edge at logic input r/o. the logic output does not switch to 1 until the time has expired.



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