ANS2 - E C E 4 1 7 5 Q U IZ 1 1-7-0 8(1 o f 2 SIX PR O B L...

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ECE 4175 QUIZ 11-7-08 (1 of 2) High 100 SIX PROBLEMS Upper quarter 89 Open book, open notes Median 78 Lower quarter 63 Low 45 1. Consider the circuit of Part A of the Design Project and the effect of the use of the 22 k S pullup resistor between the interrupt pins of the two microcontrollers. The 690_DP.c code causes this line to be pulled [20%] low for just two microseconds for each press of the pushbutton connected to the 690. (Greg Koo and David Richardson had correct answers for all four parts of this problem.) a. W hat is the average current, expressed in microamperes, in this 22 k S resistor over the loop time when the CPU detects a newly pressed pushbutton? Show all work clearly. Instantaneous current = 3V/22k S = 136 : A Loop current = 16 ms = 16000 : s Average current = (2/16000)x136 = 0.017 : A b. If Mr. Fastfingers were to press and release the pushbutton repeatedly so as to cause the 690_DP.c code to produce interrupt pulses at the maximum rate, then what would this rate be? Press and release the pushbutton so that every other looptime the 690 sees a newly pressed key; that is, every 32ms. So this rate is 1000ms/32ms = 31 presses/sec, c. W hat is the average current in this 22 k S resistor while this is going on? Since the pulse occurs every other loop time, the answer here is ½ the answer in part a, i.e., 0.0085 : A d. On the other hand, if Mr. Slowfingers presses and releases the pushbutton repeatedly so as to cause the
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