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PIC16LC554 数据表(PDF) 37 Page - Microchip Technology |
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PIC16LC554 数据表(HTML) 37 Page - Microchip Technology |
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37 / 96 page  © 1997 Microchip Technology Inc. Preliminary DS40143B-page 37 PIC16C55X(A) 7.2 Oscillator Configurations 7.2.1 OSCILLATOR TYPES The PIC16C55X(A) can be operated in four different oscillator options. 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 7.2.2 CRYSTAL OSCILLATOR / CERAMIC RESONATORS In XT, LP or HS modes a crystal or ceramic resonator is connected to the OSC1 and OSC2 pins to establish oscillation (Figure 7-2). The PIC16C55X(A) 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 pin (Figure 7-3). FIGURE 7-2: CRYSTAL OPERATION (OR CERAMIC RESONATOR) (HS, XT OR LP OSC CONFIGURATION) FIGURE 7-3: EXTERNAL CLOCK INPUT OPERATION (HS, XT OR LP OSC CONFIGURATION) See Table 7-1 and Table 7-2 for recommended values of C1 and C2. Note: A series resistor may be required for AT strip cut crystals. C1 C2 XTAL OSC2 RS OSC1 RF SLEEP To internal logic PIC16C55X(A) see Note Clock from ext. system PIC16C55X(A) OSC1 OSC2 Open TABLE 7-1: CAPACITOR SELECTION FOR CERAMIC RESONATORS (PRELIMINARY) TABLE 7-2: CAPACITOR SELECTION FOR CRYSTAL OSCILLATOR (PRELIMINARY) Ranges Characterized: Mode Freq OSC1(C1) OSC2(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 8.0 MHz 16.0 MHz 10 - 68 pF 10 - 22 pF 10 - 68 pF 10 - 22 pF 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 man- ufacturer for appropriate values of external components. Resonators to be Characterized: 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% 16.0 MHz Murata Erie CSA16.00MX ±0.5% All resonators used did not have built-in capacitors. Mode Freq OSC1(C1) OSC2(C2) LP 32 kHz 200 kHz 68 - 100 pF 15 - 30 pF 68 - 100 pF 15 - 30 pF XT 100 kHz 2 MHz 4 MHz 68 - 150 pF 15 - 30 pF 15 - 30 pF 150 - 200 pF 15 - 30 pF 15 - 30 pF HS 8 MHz 10 MHz 20 MHz 15 - 30 pF 15 - 30 pF 15 - 30 pF 15 - 30 pF 15 - 30 pF 15 - 30 pF Higher capacitance increases the stability of the 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 specification. Since each crystal has its own characteristics, the user should consult the crystal manu- facturer for appropriate values of external components. Crystals to be Characterized: 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 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 20.0 MHz ECS ECS-200-S-4 ± 50 PPM |
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