Master Control Reset Instruction (MCR)

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The Master Control Reset (MCR) instruction is used in pairs to create zones that clear all set outputs within that zone; i.e., it turns off all the non-retentive outputs in the zone. Non-Retentive outputs do not retain their memory when de-energized and are reset. The rungs contained within the two MCR commands called a zone are still scanned, but the scan time is reduced due to the false state of non-retentive outputs.

The symbol for the Master Control Reset command is illustrated above. The MCR command AB button for MCR command is placed on the right side of the rung. This output instruction is used to set up areas or "zones" of your ladder program where all non-retentive outputs may be disabled at the same time for the same length of time. MRC's are used in pairs, one MCR is used to define the start of the ladder area to be affected and one MCR to define the end of the area.
An input instruction is programmed on the rung of the first MCR to control rung logic continuity. When the rung goes "false" all set outputs within that zone are scanned as false i.e. all non-retentive outputs within the controlled zone are disabled. When the rung goes "true" all rungs are scanned according to their normal rung conditions.

The Master Control Reset ID numbers, -32,768 to +32,767, are assigned to the MCR command by positioning the cursor to the right of the Master Control Reset ID in the command and then double clicking the left mouse button. This opens a text box so that the constant value for the source may be typed.

The ending MCR instruction must be the only instruction on the rung.


Example Problem

Use the MCR command to isolate a section of a program.

In this example, when I:1/1 is TRUE the Master Control Reset command allows normal scan with normal effects on the outputs. A false input to the first MCR command, disables any outputs within the zone (O:2/1).

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