Since we can source a maximum of 20mA per pin for PORTB and total maximum source current of PORTB is 100mA, hence we can use PORTB to drive LED display directly. As shown in the circuit, 2 common cathode 7-segment LEDs are connected to PORTB with 120 Ohms current limit- ing resistor. Each segment of two LED are tied in parallel to P1. Q1 and Q2 are activated by logic high of PA0 and PA1 which switch on ground to the respective common cathode pins. PA2 and PA3 pin are use to read the inputs S1 or S2 switches.

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EXERCISES

Assignment 1 :
The two 7-segment LED now is made to display 00 simultaneously and starting counting up automatically by incrementingby one with a one second delay between each increment. When count reach 99, it should reset itself to 00 and repeat all over again

Assignment 2 :
This is a modification to Asignment 1 where the increment by one is executed only when S1 switch is pressed. When the switch is released, the increment stops. When S2 switch is pressed, it initiate a decrement by one. When count is 99, and S1 is pressed, it becomes 00. When the count is 00, and S1 is pressed, it will becomes 99.