3.3 Master Clear (MCLR) Pin

The MCLR pin provides two specific device functions:

  • Device Reset
  • Device Programming and Debugging

During device programming and debugging, the resistance and capacitance that can be added to the pin must be considered. Device programmers and debuggers drive the MCLR pin. Consequently, specific voltage levels (VIH and VIL) and fast signal transitions must not be adversely affected. Ensure that the MCLR pin VIH and VIL voltage specifications are met.

For example, Figure 3-2 shows the MCLR pin connections with general circuit components used, such as resistor R, series resistor R1 and capacitor C, and their placement. It is recommended to place these passive components within one-quarter inch (6mm) from the MCLR pin.

Figure 3-2. Example of MCLR Pin Connections
Note:
  1. R ≤ 10 kΩ is recommended. A suggested starting value is 10 kΩ. Ensure that the MCLR pin VIH and VIL specifications are met.
  2. R1 ≤ 470Ω will limit 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). Ensure that the MCLR pin VIH and VIL specifications are met.
  3. C ≤ 1 µF may be recommended. However, values of C should be based on reset timings required for any application. Make sure to isolate C from the MCLR pin during programming and debugging operations.