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Homework Statement
LOGIC DESIGN USING MSI COMPONENTS
A small corporation has 10 shares of stock, and each share entitles its owner to one vote at a stockholder’s meeting. The 10 shares of stock are owned by four people as follows:
Mr.W; 1 share, Mr. X; 2 shares, Mr. Y; 3 shares, Mrs. Z; 4 shares.
Each of these persons has a switch to close when voting yes and to open when voting no for all his/her shares (one switch for each person).
Task: It is necessary to design a circuit (using MSI components ONLY, a 7-segment display and some inverters if required) that displays the total number of shares that vote YES for each measure.
If all shares vote NO for a measure, the display should be blank. If ten shares vote YES for a measure, the display should be 0, otherwise, the display shows a decimal number equal to the number of shares that vote YES.
Use 74151 multiplexers to design the combinational logic that converts the input from stockowners (ON-YES, OFF-NO) switches into the BCD digit for the 7-segment decoder/driver. Choose W to be the MSB, X, Y, Z to be selection lines of the MUX’s.
The Attempt at a Solution
The attached circuit from Circuitmaker shows how I have wired the multiplexers, however I am stuck! I can get the correct output for most cases except when the 1 is involved in the output - 10 (needs to display 0), 8 (4 + 3 + 1), 6 (3 + 2 + 1), 4 (3 + 1) and 0 (needs to set an illegal code on 4511) don't work. I can see why they don't work, but not how to fix it. I'm going to have to look at inverters, but haven't got a clue where to start, and have been unable to find anything I could understand re: Karnaugh maps. Mature student, thrown back in at the deep end on this question (last one on the assignment), with no tutorials on multiplexers whatsoever! Any help appreciated.
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