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PIC16F84A 数据表(PDF) 39 Page - Microchip Technology |
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PIC16F84A 数据表(HTML) 39 Page - Microchip Technology |
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39 / 124 page  PIC16F8X © 1998 Microchip Technology Inc. DS30430C-page 39 8.2 Oscillator Configurations 8.2.1 OSCILLATOR TYPES The PIC16F8X can be operated in four different oscillator modes. The user can program two configuration bits (FOSC1 and FOSC0) to select one of these four modes: • LP Low Power Crystal • XT Crystal/Resonator • HS High Speed Crystal/Resonator • RC Resistor/Capacitor 8.2.2 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 8-3). FIGURE 8-3: CRYSTAL/CERAMIC RESONATOR OPERATION (HS, XT OR LP OSC CONFIGURATION) The PIC16F8X 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 to drive the OSC1/CLKIN pin (Figure 8-4). FIGURE 8-4: EXTERNAL CLOCK INPUT OPERATION (HS, XT OR LP OSC CONFIGURATION) TABLE 8-1 CAPACITOR SELECTION FOR CERAMIC RESONATORS TABLE 8-2 CAPACITOR SELECTION FOR CRYSTAL OSCILLATOR Note1: See Table 8-1 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. C1(1) C2(1) XTAL OSC2 OSC1 RF(3) SLEEP To logic PIC16FXX RS(2) internal OSC1 OSC2 Open Clock from ext. system PIC16FXX Ranges Tested: Mode Freq OSC1/C1 OSC2/C2 XT 455 kHz 2.0 MHz 4.0 MHz 47 - 100 pF 15 - 33 pF 15 - 33 pF 47 - 100 pF 15 - 33 pF 15 - 33 pF HS 8.0 MHz 10.0 MHz 15 - 33 pF 15 - 33 pF 15 - 33 pF 15 - 33 pF Note : Recommended values of C1 and C2 are identical to the ranges tested table. Higher capacitance increases the stability of the oscillator but also increases the start-up time. These values are for design guidance only. Since each resonator has its own characteristics, the user should consult the resonator manufacturer for the appropriate values of external components. Resonators Tested: 455 kHz Panasonic EFO-A455K04B ± 0.3% 2.0 MHz Murata Erie CSA2.00MG ± 0.5% 4.0 MHz Murata Erie CSA4.00MG ± 0.5% 8.0 MHz Murata Erie CSA8.00MT ± 0.5% 10.0 MHz Murata Erie CSA10.00MTZ ± 0.5% None of the resonators had built-in capacitors. Mode Freq OSC1/C1 OSC2/C2 LP 32 kHz 200 kHz 68 - 100 pF 15 - 33 pF 68 - 100 pF 15 - 33 pF XT 100 kHz 2 MHz 4 MHz 100 - 150 pF 15 - 33 pF 15 - 33 pF 100 - 150 pF 15 - 33 pF 15 - 33 pF HS 4 MHz 10 MHz 15 - 33 pF 15 - 33 pF 15 - 33 pF 15 - 33 pF Note : Higher capacitance increases the stability of oscillator but also increases the start-up time. 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 spec- ification. Since each crystal has its own characteris- tics, the user should consult the crystal manufacturer for appropriate values of external components. For VDD > 4.5V, C1 = C2 ≈ 30 pF is recommended. Crystals Tested: 32.768 kHz Epson C-001R32.768K-A ± 20 PPM 100 kHz Epson C-2 100.00 KC-P ± 20 PPM 200 kHz STD XTL 200.000 KHz ± 20 PPM 1.0 MHz ECS ECS-10-13-2 ± 50 PPM 2.0 MHz ECS ECS-20-S-2 ± 50 PPM 4.0 MHz ECS ECS-40-S-4 ± 50 PPM 10.0 MHz ECS ECS-100-S-4 ± 50 PPM |
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