What is MRES Switch?
- A PLC’s “MRES” switch denotes “Memory Reset.”
- By using this switch, the PLC’s memory can be reset to its default (or) uninitialized state, erasing any stored programs or data.
- This feature is helpful when programming or troubleshooting PLCs because it lets you restart or undo any accidental modifications to the data or program that was stored in memory.
- This switch will remove all stored data, so it’s essential to use caution when using it. If done incorrectly, this could result in the loss of crucial data or programs.
- MRES switch is frequently seen on Siemens PLCs such as the S7-300 series.
- This particular mode is used to reset memory on the PLC’s physical switch located on the CPU (Central Processing Unit).
MRES Function
- A PLC memory reset is triggered by the MRES switch, which is engaged by keeping it in the MRES position for a predetermined amount of time.
- Through this reset procedure, the PLC’s work memory is cleared, encompassing:
- Program for the user (function blocks, ladder logic, etc.)
- Temporary information (values kept while a program executes)
- However, it has no significance on if this memory is configured in the software, certain data values are kept there even after resets or power cycles.
- The MRES reset has no effect on the contents of an external memory card used by the PLC.
Applications of MRES Switch
- MRES is frequently used as a stage in the troubleshooting process to eliminate possible program mistakes or unusual PLC performance.
- The MRES reset may be used to force a restart of the PLC in cases when it is stuck or unresponsive, possibly fixing the problem.
In conclusion, the MRES switch on a PLC is an effective tool for memory reset, but in order to prevent unexpected effects, it should be used carefully and with understanding of its implications.