CEG3136DGD3Solution.pdf - CEG 3136 Computer Architecture II...

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CEG 3136 Computer Architecture II Tutorial 3 The Parallel Ports Fall 2017 Consider loading the values in to the following registers as shown below: DDRA: Binary value 11110000 PORTA: Binary value 00000000 1) If PUPAE in the PUCR register is set to 0, what can be said about the voltage levels that will appear at PA0 to PA3? If no key is pressed , the voltage levels on pins PAx (x=0,1,2,3,4) will float as there is no active element connected to the pins that drive the voltages to any level. If a key linked between Col_x (x = 0,1,2,3) and Row_y (y = 0,1,2,3) is pressed , a connection will be made from pin PAx (a PORTA input) to the corresponding Row_y line (y = 0,1,2,3) linked to a PORTA output. Since PORTA=%0000 0000 (PA(y+4)=0), Row_y line is connected to ground, and the voltage at pin PAx will be subsequently 0. If Row_y lines would be connected to +5V (PORTA = %1111 0000 , i.e., PA(y+4) = 1), then the voltage at PAx would be +5V. What if PUPA is set to 1? If no key is pressed , the voltage levels at the pins PAx will be 5V since pullup resistors have been activated ( PUPAE = 1) and will drive the pins to this level.
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