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ECEN 248
Lab 6: De-Bouncing, Counters &
LCD Display Control
Dept. of Electrical and Computer
Engineering
Lab 6 in Brief

Design an eight bit counter
 Bouncing
counter
 De-bouncing counter

Learn about configuring the LCD display
Sequential Logic




We are only handling the combinational
logic circuits in the previous labs
Starting from Lab 5, we will deal with the
sequential logic circuits
In sequential logic circuits, the output will
depend on not only the current input, but
also the previous inputs.
Always driven by clock pulses
Counter

Using sequential logic to count clock
events
Push Buttons
A push button is a mechanical switch and rely on
mechanical contact to generate an electrical pulses
Switch Bouncing
When you push the button, it will not instantly give a
0 (or a 1 when inverted); instead, the voltage will
fluctuate in a middle region at first. Voltages in the
middle region are still interpreted (quantized) as 1’s
and 0’s, so the output will “bounce” between 0 and 1
until the value settles.
 That means even you only push the button once,
there will be multiple rising edges generated.

Push
Release
De-Bouncing


Need to get rid of the bounces and get the
“clean” signal
Two methods
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
RS latch based debouncing

Needs two buttons

One button
Sampling based de-bouncing
Method 1: SR Latch
Bouncing
• Use the SR latch to clean the
bouncing signal
S
R
Q
De-bounced
Method 2: Sampling based debouncing
always @ (posedge clock)
if (reset) begin new <= noisy; clean <= noisy; count <= 0; end
else if (noisy != new) begin new <= noisy; count <= 0; end
else if (count == 500000) clean <= new;
else count <= count+1;
LCD Display
•Two Verilog modules
•lcd_disp
•Given in the zip file for lab 5
•You can reuse this module
•Lcd_int
•You need to design a specific lcd_int module for each lab
•Determine data display location in LCD
•One characters  8bit (check decoder chart Fig. 6.9)
•Outputs 32 eight-bit sequences for 32 characters in LCD
Lab 6 To-Do list


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Design 1
 Configure LCD display
Design 2
 Design a non-debounced counter
Design 3
 Design a count-up counter and a count-down
counter using non-debounced signal
Design 4
 Design a SR-latch based debounced up-counter
Design 5
 Design a sampling-based debounced up-counter
Deadlines

Today


Work on Lab 6
2 Weeks later


Lab 6 Post-Lab due
Lab 7 Pre-Lab due at the beginning of class

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