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CF745 数据表(PDF) 33 Page - Microchip Technology |
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CF745 数据表(HTML) 33 Page - Microchip Technology |
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33 / 217 page  © 1998 Microchip Technology Inc. Preliminary DS30453B-page 33 PIC16C5X 7.2 Oscillator Configurations 7.2.1 OSCILLATOR TYPES PIC16C5Xs can be operated in four different oscillator modes. The user can program two configuration bits (FOSC1:FOSC0) to select one of these four modes: • LP: Low Power Crystal • XT: Crystal/Resonator • HS: High Speed Crystal/Resonator • RC: Resistor/Capacitor 7.2.2 CRYSTAL OSCILLATOR / CERAMIC RESONATORS In XT, LP or HS modes, a crystal or ceramic resonator is connected to the OSC1/CLKIN and OSC2/CLKOUT pins to establish oscillation (Figure 7-3). The PIC16C5X oscillator design requires the use of a parallel cut crystal. Use of a series cut crystal may give a frequency out of the crystal manufacturers specifications. When in XT, LP or HS modes, the device can have an external clock source drive the OSC1/CLKIN pin (Figure 7-4). FIGURE 7-3: CRYSTAL OPERATION (OR CERAMIC RESONATOR) (HS, XT OR LP OSC CONFIGURATION) Note: Not all oscillator selections available for all parts. See Section 7.1. Note 1: See Capacitor Selection tables for recommended values of C1 and C2. 2: A series resistor (RS) may be required for AT strip cut crystals. 3: RF varies with the crystal chosen (approx. value = 10 M Ω). C1(1) C2(1) XTAL OSC2 OSC1 RF(3) SLEEP To internal logic RS(2) PIC16C5X FIGURE 7-4: EXTERNAL CLOCK INPUT OPERATION (HS, XT OR LP OSC CONFIGURATION) TABLE 7-1: CAPACITOR SELECTION FOR CERAMIC RESONATORS - PIC16C5X, PIC16CR5X TABLE 7-2: CAPACITOR SELECTION FOR CRYSTAL OSCILLATOR - PIC16C5X, PIC16CR5X Osc Type Resonator Freq Cap. Range C1 Cap. Range C2 XT 455 kHz 2.0 MHz 4.0 MHz 22-100 pF 15-68 pF 15-68 pF 22-100 pF 15-68 pF 15-68 pF HS 4.0 MHz 8.0 MHz 16.0 MHz 15-68 pF 10-68 pF 10-22 pF 15-68 pF 10-68 pF 10-22 pF Note: These values are for design guidance only. Since each resonator has its own charac- teristics, the user should consult the reso- nator manufacturer for appropriate values of external components. Osc Type Resonator Freq Cap.Range C1 Cap. Range C2 LP 32 kHz(1) 100 kHz 200 kHz 15 pF 15-30 pF 15-30 pF 15 pF 30-47 pF 15-82 pF XT 100 kHz 200 kHz 455 kHz 1 MHz 2 MHz 4 MHz 15-30 pF 15-30 pF 15-30 pF 15-30 pF 15-30 pF 15-47 pF 200-300 pF 100-200 pF 15-100 pF 15-30 pF 15-30 pF 15-47 pF HS 4 MHz 8 MHz 20 MHz 15-30 pF 15-30 pF 15-30 pF 15-30 pF 15-30 pF 15-30 pF Note 1: For VDD > 4.5V, C1 = C2 ≈ 30 pF is recommended. 2: These values are for design guidance only. Rs may be required in HS mode as well as XT mode to avoid overdriving crystals with low drive level specification. Since each crystal has its own characteristics, the user should consult the crystal manufacturer for appropriate values of external components. Note: If you change from this device to another device, please verify oscillator characteristics in your application. Clock from ext. system OSC1 OSC2 PIC16C5X Open |
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