A seven-segment display is the type of familiar display most often seen in older digital clocks and electronic equipment, most often through the 4511 chip. Each of its segments is labeled by a letter, A through G. Letter A is the top segment, and B through F continue clockwise around the display, with B at the top right and F at the top left. Letter G is the center segment.The logic circuits for
. this display come in two forms: decimal and hexadecimal. The decimal form represents the numbers 0 through 9. The hexadecimal form also represents these numbers, but it also represents the hexadecimal digits A through F, which are not to be confused for the segments themselves. The digit B (11 in decimal) must be represented by a lower-case b, and the digit D (13 in decimal) must similarly be lower-case; otherwise, they would look like an 8 and 0, respectively. Other hexadecimal digits are almost always represented in upper case.The input to these circuits is in binary code, separated into the numbers 1, 2, 4 and 8. Each signal goes through a complicated series of AND, OR, NOT and other gates to determine the final output of the seven segments. For example, if the number 1 is represented, only the binary 1 is on; 2, 4 and 8 are off. This leads to segments B and C being lit up, while all other segments are dark. If both binary 1 and 2 are on, segments A, B, C, D and G are lit, displaying the number 3. However, if binary 4 is then turned on, segments are turned off to form the number 7. Other inputs to this circuit exist that are not numbers, but rather commands to do things like light up the entire display or blank it.The logic gates themselves are best depicted visually, and the following links show diagrams of these circuits. More reference links: http://hibp.ecse.rpi.edu/~connor/education/IEE/lectures/Lecture_7_digital_display.pdf http://www.allaboutcircuits.com/vol_6/chpt_7/9.html
