1. Lab 12 : Liquid Crystal Displays: Slide #2 Slide #3 7-Segment LCD: XOR gate review 7-Segment LCD: System Operation

2. Start at the the first section B=1 and A=0. For an XOR gate the response is Y=1. Draw Y for that section. The next section B=0 and A=0. For an XOR gate the response is Y=0. Draw Y for that section. The next section B=0 and A=1. For an XOR gate the response is Y=1. Draw Y for that section. The next section B=1 and A=1. For an XOR gate the response is Y=0. Draw Y for that section. Continue to use this technique to complete the drawing of output waveform Y. Now that the waveform is drawn we can proceed to a more general discussion of the controlled inverter system. Control Switch 5v A B Y Lab 12: XOR gates as Controlled Inverters: A 7-segment LCD display system uses 7 Xor gates configured as controlled inverters. The position of the Control Switch is represented by waveform A. When A=0 the switch is in the lower position. When A=1 the switch is in the upper position. Proceed to view the animation. B A To draw the output response (Y) it is helpful to draw vertical lines at each transition of waveform A and B. Y The vertical lines create horizontal sections. These sections will be used to determine the output response. The XOR gate passes the Data from input B (non inverted) when the Control Switch is 0. The XOR gate passes the INVERSE of the Data from input B when the Control Switch is 1. The switch controls the inversion of the data from input B! ABX 000 011 101 110 Slide #2

3. Lab 12: 7-Segment LCD System : The 7-segment LCD display system uses seven XOR controlled inverters. The XOR control switch is replaced by the segment output(a, b, …,g) of the display decoder. When the XOR passes the INVERSE of the Pulse waveform the segment will be visible. The number 7 will be used to demonstrate the system operation. It is applied to inputs A, B, C, D. 11101110 The decoder responds by asserting segments a, b, c. These segments are required to display 7. 1 1 1 0 0 0 0 The a, b, c segments act as a control switch at logic 1. The XOR gates pass the inverse of the 30 PPS pulse waveform. The d, e, f, g segments act as a control switch at logic 0. The XOR gates pass the 30 PPS pulse waveform (non inverted). The 30 PPS pulse from the XOR gates creates a 0V potential difference between the back plane (BP) and the segment. This makes the segment NOT visible! BP = 5V & Segment = 5V. BP = 0V & Segment = 0V. The inverse 30 PPS pulse from the XOR gates creates a 5V potential difference between the back plane (BP) and the segment. This makes the segment visible! BP = 5V & Segment = 0V. BP = 0V & Segment = 5V. Slide #3 Note: Decoder has active high outputs