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W78L801P-24 Datasheet(PDF) 10 Page - Winbond |
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W78L801P-24 Datasheet(HTML) 10 Page - Winbond |
10 / 20 page W78L801 - 10 - Clock The W78L801 is designed to be used with either a crystal oscillator or an external clock. Internally, the clock is divided by two before it is used. This makes the W78L801 relatively insensitive to duty cycle variations in the clock. The W78L801 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. An external clock source 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. Power Management Idle Mode The idle mode is entered by setting the IDL bit in the PCON register. 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. 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 INT2 to INT9 when enabled. AUXR - Auxiliary Register Bit: 7 6 5 4 3 2 1 0 - - - - - - - AO Mnemonic: AUXR Address: 8Eh AO: Turn off ALE signal. Reduce EMI Emission Because of the on-chip ROM, when a program is running in internal ROM space, the ALE will be unused. The transition of ALE will cause noise, so it can be turned off to reduce the EMI emission if it is not needed. Turning off the ALE signal transition only requires setting the bit 0 of the AUXR SFR, which is located at 08Eh. When ALE is turned off, it will be reactivated when the program accesses external ROM/RAM data or jumps to execute an external ROM code. The ALE signal will turn off again after it has been completely accessed or the program returns to internal ROM code space. 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 W78L801 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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