ANSFB - E C E 4 1 7 5 B F in a l 5 -5 -1 0 E I GH T PR O B...

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ECE 4175B Final 5-5-10 1 of 3 High 107 EIGHT PROBLEMS Upper quarter 88 Open book, open notes Median 78 Lower quarter 68 Low 53 1. Assume that you have set up the “extended input capture” mode described on the back of the review sheet for this final exam using the CCP1/Timer1 combination plus a RAM variable, TMR1X to capture a 24-bit [10%] time stamp when a rising edge occurs on the CCP1 input pin. When this edge occurs, assume that once the high-priority interrupt service routine has been called, both the TMR1IF flag and the CCP1IF flag are set. a. What does this indicate? An input edge occurred at about the same time that Timer1 rolled over from FFFF to 0000. b. Under what circumstances does the time stamp consist of the content of TMR1X:CCPR1H:CCPR1L as they are at the moment that the high-priority interrupt service routine is entered with both flags set? Explain your answer. If the time captured was before Timer1 rolled over (tested by the most-significant bit of CCPR1H = 1). c. On the other hand, under what circumstances does the time stamp not consist of the content of TMR1X:CCPR1H:CCPR1L as they are at the moment that the high-priority interrupt service routine is entered with both flags set? Explain your answer. If the time captured was when Timer1 = 0000 or later (tested by MSb of CCPR1H = 0). 2. For their design project, one team used the output from a two-axis accelerometer to control the pixel-by- pixel movement of an “etch-a-sketch” display on the 24x2 character LCD. One axis of the output [15%] controlled vertical movement of the sketch, turning on a pixel either above or below the last pixel (for up to sixteen vertical pixel positions). The other axis output controlled horizontal movement, adding to the figure by turning on the next pixel to the left or right. They used an Nx2 block of character positions to contain their otherwise arbitrary display of turned on pixels. a. How big a block of Nx2 character positions of their LCD could they define for this use? N = 4 so Nx2 = 8 since there are just eight user-defined characters available b. To implement this display, they employed the LCD’s user-defined character capability with a table stored in RAM to hold the characters. How many bytes of RAM were required for this table? Each user-defined character requires eight bytes of RAM. Putting eight of these into a
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This note was uploaded on 02/08/2011 for the course ECE 4175 taught by Professor Peatman during the Spring '08 term at Georgia Tech.

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ANSFB - E C E 4 1 7 5 B F in a l 5 -5 -1 0 E I GH T PR O B...

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