12.3 Fail-Safe Clock Monitor (FSCM)

The Fail-Safe Clock Monitor (FSCM) allows the device to continue operating in the event of an oscillator failure. The FSCM also provides diagnostic data pertaining to potential primary and secondary oscillator failures. The FSCM serves three separate functions:

  • Monitoring of FOSC using the FSCMFEV bit
  • Monitoring of EXTOSC (primary external oscillator) using the FSCMPEV bit
  • Monitoring of SOSC (secondary external oscillator) using the FSCMSEV bit

The primary external oscillator FSCM (FSCMP) is enabled by setting the Fail-Safe Clock Monitor for Primary Crystal Oscillator (FCMENP) Configuration bit. The secondary external oscillator FSCM (FSCMS) is enabled by setting the Fail-Safe Clock Monitor for Secondary Crystal Oscillator (FCMENS) Configuration bit. The FOSC FSCM is enabled by setting the Fail-Safe Clock Monitor Enable for FOSC (FCMEN) Configuration bit. The figure below shows the FSCM block diagram.

Figure 12-10. FSCM Block Diagram