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Unformatted text preview: solve this problem, the circuit in Figure 4.1.2 can be considered. Now, the state is clearly ‘high’ when the switch is ‘open’, but shorts arise when the switch is ‘closed’ as VCC (power) is directly connected to GND (ground). Eventually, Figure 4.1.3 presents the third type of switch input circuit that uses a pull-up resistor in order to prevent shorts and to ensure that inputs to logic systems settle at expected logic levels if devices are disconnected. In this circuit, the state is ‘low’ when the switch is ‘closed’ (ON) , and ‘high’ with the switch ‘open’ (OFF). Figure 4.1.1 Switch Input Circuit (Type 1) Figure 4.1.2 Switch Input Circuit (Type 2) Figure 4.1.3 Switch Input Circuit (Type 3) 4.1.2 Crystal Oscillator A crystal oscillator, often abbreviated OSC and also known as x-tal, is an electronic circuit that creates an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time, to provide a stable clock signal for digital integra...
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- Spring '10