5.2.1.1 EC Mode

The External Clock (EC) mode allows an externally generated logic level signal to be the system clock source. When operating in this mode, an external clock source is connected to the OSC1 input. OSC2/CLKOUT is available for general purpose I/O or CLKOUT. The following figure shows the pin connections for EC mode.

EC mode has three power modes to select from through Configuration Words:

  • ECH – High power, above 16 MHz
  • ECM – Medium power, 100 kHz to 16 MHz
  • ECL – Low power, below 100 kHz

The Oscillator Start-up Timer (OST) is disabled when EC mode is selected. Therefore, there is no delay in operation after a Power-on Reset (POR) or wake-up from Sleep. Because the PIC® MCU design is fully static, stopping the external clock input will have the effect of halting the device while leaving all data intact. Upon restarting the external clock, the device will resume operation as if no time had elapsed.

Figure 5-2. External Clock (EC) Mode Operation
Note:
  1. Output depends upon CLKOUTEN bit of the Configuration Words (CONFIG1H).