8.2.1.2 LP, XT, HS Modes

The LP, XT and HS modes support the use of quartz crystal resonators or ceramic resonators connected to OSC1 and OSC2 (Figure 8-3). The three modes select a low, medium or high gain setting of the internal inverter-amplifier to support various resonator types and speed.

LP Oscillator mode selects the lowest gain setting of the internal inverter-amplifier. LP mode current consumption is the least of the three modes. This mode is designed to drive only 32.768 kHz tuning-fork type crystals (watch crystals). but can operate up to 100 kHz.

XT Oscillator mode selects the intermediate gain setting of the internal inverter-amplifier. XT mode current consumption is the medium of the three modes. This mode is best suited to drive crystals and resonators with a frequency range up to 4 MHz.

HS Oscillator mode selects the highest gain setting of the internal inverter-amplifier. HS mode current consumption is the highest of the three modes. This mode is best suited for resonators that require operating frequencies up to 20 MHz.

Figure 8-3 and Figure 8-4 show typical circuits for quartz crystal and ceramic resonators, respectively.

Figure 8-3. Quartz Crystal Operation (LP, XT or HS Mode)
Figure 8-4. Ceramic Resonator Operation (XT or HS Mode)
Note:
  1. Quartz crystal characteristics vary according to type, package and manufacturer. The user may consult the manufacturer data sheets for specifications and recommended application.
  2. Always verify oscillator performance over the VDD and temperature range that is expected for the application.
  3. For oscillator design assistance, reference the following Microchip application notes:
    • AN826, “Crystal Oscillator Basics and Crystal Selection for PIC® and PIC® Devices” (DS00826)
    • AN849, “Basic PIC® Oscillator Design” (DS00849)
    • AN943, “Practical PIC® Oscillator Analysis and Design” (DS00943)
    • AN949, “Making Your Oscillator Work” (DS00949)