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MCRA/MCRD : Master Control Relay Activate/Deactivate



Important Notes on Using MCR Functions





Symbol





MCRA









MCR Activate



With the Activate Master Control Relay, instruction, you make subsequent commands dependent on the MCR. After entering this command, you can program the MCR zones with these instructions (see Master Control Relay On/Off). When your program activates an MCR area, all MCR actions depend on the content of

the MCR stack.





Symbol





MCRD









MCR Deactivate



With the Deactivate Master Control Relay instruction, subsequent commands are no longer dependent on the MCR. After this instruction, you cannot program any more MCR zones. When your program deactivates an MCR area, the MCR is always energized irrespective of the entries in the MCR stack.



The MCR stack and the bit that controls its dependency (the MA bit) relate to individual levels and must be saved and fetched every time you change the sequence level. They are preset at the beginning of every sequence level (MCR input bits 1 to 8 are set to 1, the MCR stack pointer is set to 0 and the MA bit is set to 0).



The MCR stack is transferred from block to block and the MA bit is saved and set to 0 every time a block is called. It is fetched back at the end of the block.



The MCR can be implemented in such a way that it optimizes the run time of code- generating CPUs. The reason for this is that the dependency of the MCR is not passed on by the block; it must be explicitly activated by an MCR instruction. A code-generating CPU recognizes this instruction and generates the additional code necessary for the evaluation of the MCR stack until it recognizes an MCR instruction or reaches the end of the block. With instructions outside the MCRA/MCRD range, there is no increase of the run time.



The instructions MCRA and MCRD must always be used in pairs within your program.


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