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lab5_f10 - University of Florida ECE Dept Page 1/2 EEL 4744...

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University of Florida EEL 4744 Dr. Gugel ECE Dept. Page 1/2 9/23/10 - 5:56 PM Lab #5: Software Switch Debounce & Adding an 8 Bit External Output Port Purpose This lab consists of two parts. The first is to create de-bounce software for the keypad added in Lab #4 to use the keypad as a counter. The second part is to add an external port to the DSP using an 8 bit latch (74HC574). In order to add this latch, we will need to place it in the memory map of the DSP and modify the CPLD to implement the required decode equation. Both the de-bounce software and external port must be complete by the end of this lab. Part I. De-boucing a Switch via Software In Lab #4, you added a keypad to your DSP development board and wrote software to display the key pressed on your LED binary display. We will now use the same hardware as before and only modify the software to do the following: 1. Check when the "1", “2” or “3” keys are pressed on your keypad (one at a time). 2. Every time the "1" key is pressed, increment a once counter and display on your LED display. Every time the “2” key is pressed, increment your counter value by 2 and display. Every time the “3” key is pressed, increment your counter by 3 and display. The counter/display should be an eight bit value. 3. If a "0" is pressed, zero out the counter value. Because we are now counting the number of keystrokes, we will need to de-bounce the keypad switches. This step is necessary because when a key is pressed or released, the contacts of the switch bounce between the switch being open and closed repeatedly for several milliseconds (typically 1-25 mSec).
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