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PIC16F87 Datasheet(PDF) 77 Page - Microchip Technology |
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PIC16F87 Datasheet(HTML) 77 Page - Microchip Technology |
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77 / 228 page  2005 Microchip Technology Inc. DS30487C-page 75 PIC16F87/88 7.6 Timer1 Oscillator A crystal oscillator circuit is built between pins T1OSI (input) and T1OSO (amplifier output). It is enabled by setting control bit T1OSCEN (T1CON<3>). The oscilla- tor is a low-power oscillator, rated up to 32.768 kHz. It will continue to run during all power-managed modes. It is primarily intended for a 32 kHz crystal. The circuit for a typical LP oscillator is shown in Figure 7-3. Table 7-1 shows the capacitor selection for the Timer1 oscillator. The user must provide a software time delay to ensure proper oscillator start-up. FIGURE 7-3: EXTERNAL COMPONENTS FOR THE TIMER1 LP OSCILLATOR TABLE 7-1: CAPACITOR SELECTION FOR THE TIMER1 OSCILLATOR 7.7 Timer1 Oscillator Layout Considerations The Timer1 oscillator circuit draws very little power during operation. Due to the low-power nature of the oscillator, it may also be sensitive to rapidly changing signals in close proximity. The oscillator circuit, shown in Figure 7-3, should be located as close as possible to the microcontroller. There should be no circuits passing within the oscillator circuit boundaries other than VSS or VDD. If a high-speed circuit must be located near the oscilla- tor, a grounded guard ring around the oscillator circuit, as shown in Figure 7-4, may be helpful when used on a single-sided PCB or in addition to a ground plane. FIGURE 7-4: OSCILLATOR CIRCUIT WITH GROUNDED GUARD RING Note: The Timer1 oscillator shares the T1OSI and T1OSO pins with the PGD and PGC pins used for programming and debugging. When using the Timer1 oscillator, In-Circuit Serial Programming™ (ICSP™) may not function correctly (high voltage or low voltage), or the In-Circuit Debugger (ICD) may not communicate with the controller. As a result of using either ICSP or ICD, the Timer1 crystal may be damaged. If ICSP or ICD operations are required, the crystal should be disconnected from the circuit (disconnect either lead) or installed after programming. The oscillator loading capacitors may remain in-circuit during ICSP or ICD operation. PIC16F87/88 T1OSI T1OSO C2 33 pF C1 33 pF XTAL 32.768 kHz Note: See the Notes with Table 7-1 for additional information about capacitor selection. Osc Type Freq C1 C2 LP 32 kHz 33 pF 33 pF Note 1: Microchip suggests this value as a starting point in validating the oscillator circuit. 2: Higher capacitance increases the stability of the oscillator but also increases the start-up time. 3: Since each resonator/crystal has its own characteristics, the user should consult the resonator/crystal manufacturer for appropriate values of external components. 4: Capacitor values are for design guidance only. OSC1 VSS OSC2 RB7 RB6 RB5 |
Similar Part No. - PIC16F87_05 |
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Similar Description - PIC16F87_05 |
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