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W78ERD2A40PN Datasheet(PDF) 8 Page - Winbond |
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W78ERD2A40PN Datasheet(HTML) 8 Page - Winbond |
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8 / 72 page  W78ERD2 - 8 - 6.3 Clock The W78ERD2 is designed with either a crystal oscillator or an external clock. 6.4 Crystal Oscillator The W78ERD2 incorporates a built-in crystal oscillator. To make the oscillator work, a crystal must be connected across pins XTAL1 and XTAL2. In addition, a load capacitor must be connected from each pin to ground, and a resistor must also be connected from XTAL1 to XTAL2 to provide a DC bias when the crystal frequency is above 24 MHz. 6.5 External Clock An external clock should be connected to pin XTAL1. Pin XTAL2 should be left unconnected. The XTAL1 input is a CMOS-type input, as required by the crystal oscillator. As a result, the external clock signal should have an input one level of greater than 3.5 volts. 6.6 Power Management 6.6.1 Idle Mode Setting the IDL bit in the PCON register enters the idle mode. In the idle mode, the internal clock to the processor is stopped. The peripherals and the interrupt logic continue to be clocked. The processor will exit idle mode when either an interrupt or a reset occurs. 6.6.2 Power-down Mode When the PD bit in the PCON register is set, the processor enters the power-down mode. In this mode all of the clocks are stopped, including the oscillator. To exit from power-down mode is by a hardware reset or external interrupts INT0 to INT1 when enabled and set to level triggered. 6.7 Reduce EMI Emission If the crystal frequency is under 25 MHz, please option.b7 is set to 0 by the writer. Please refer option bits description to operate this bit. 6.8 Reset The external RESET signal is sampled at S5P2. To take effect, it must be held high for at least two machine cycles while the oscillator is running. An internal trigger circuit in the reset line is used to deglitch the reset line when the W78ERD2 is used with an external RC network. The reset logic also has a special glitch removal circuit that ignores glitches on the reset line. During reset, the ports are initialized to FFH, the stack pointer to 07H, PCON (with the exception of bit 4) to 00H, and all of the other SFR registers except SBUF to 00H. SBUF is not reset. |
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