2.2.2 Master Clear (MCLR) Pin

The MCLR pin provides for two specific device functions:
  • Device Reset
  • Device programming and debugging

Pulling the MCLR pin low generates a device Reset. The following figure illustrates a typical MCLR circuit. When programming and debugging the device, consider the resistance and capacitance that can be added to the pin. Device programmers and debuggers drive the MCLR pin. As a result, specific voltage levels (VIH and VIL) and fast signal transitions must not be adversely affected. Therefore, specific values of R and C need to be adjusted based on the application and PCB requirements.

For example, the recommendation is to isolate capacitor C from the MCLR pin during programming and debugging operations.

Place the components within one-quarter inch (6 mm) from the MCLR pin.
Figure 2-5. Example of MCLR Pin Connections
Note:

  1. 470Ω ≤ R1 ≤ 1 kΩ limits any current flowing into MCLR from the external capacitor C, in the event of MCLR pin breakdown, due to Electrostatic Discharge (ESD) or Electrical Overstress (EOS). The user must meet the MCLR pin VIH and VIL specifications without interfering with the debug/programmer tools.

  2. Size the capacitor to prevent unintentional resets from brief glitches or to extend the device Reset period during POR.