2.3 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. Therefore, specific values of R and C will need to be adjusted based on the application and PCB requirements.

For example, as shown in Figure 2-2, it is recommended that the capacitor, C, be isolated from the MCLR pin during programming and debugging operations.

Place the components, as shown in Figure 2-2, within one-quarter inch (6 mm) from the MCLR pin.

Figure 2-2. 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. This device has two MCLR pins.