The keyboard circuit of Figure 9-16 is designed to accept a three digit decimal number. What would

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The keyboard circuit of Figure 9-16 is designed to accept a three digit decimal number. What would happen if four digit keys were activated (e.g., 3095)? Design the necessary logic to be added to this circuit so that after three digits have been entered, any additional digits will be ignored until the CLEAR key is depressed. In other words, if 3095 is entered on the keyboard, the output registers will display 309 and will ignore the 5 and any subsequent digits until the circuit is cleared.


Figure 9-16

Digit keys +5V 1 k For switch bounce T OS Q Q 20 ms Pull-up resistor for each input 74LS147 decimal- to-BCD

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Digital Systems Principles And Application

ISBN: 9780134220130

12th Edition

Authors: Ronald Tocci, Neal Widmer, Gregory Moss

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