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So i've got a question to build a truth table for a controller circuit I've to build. From the wording of the question I'm unsure which of my truth tables are correct (if at all).

The controller logic circuit needs to be designed. The controller has a six-core wire connecting it to the Wi-i console and each wire carries a boolean/binary output value of 0 or 5 volts (or 0 and 1). The combination of six values on the wires controls the sprite. Inside the controller there is some circuitry to create the correct 0 or 1 value on each wire for each button combination and it is your job to design part of that circuitry. Create the truth table for the controller behaviour. Assume that the buttons when pressed individually or in combination create a 4 bit binary number, between 0000 (010) and 1111 (1510). These four bits are represented for convenience as A,B,C and D, with A representing the least significant bit. The code for each button combination can be taken to be its ordinality in the table given above. There can be six different outputs CW, ACW, L, R, U & D as indicated in Figure 1.

Figure 1

My truth tables:

Truth Tables

I guess the bit that is confusing me is the A, B, C, D labels and which button should be what. Because it states A is the least significant bit, should I use that as button 4 or button 1. Would appreciate any thoughts.

Suggested truth table from InBedded16

Truth Table 3

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  • \$\begingroup\$ If you want to score some brownie points with your instructor, you might mention that, it's very hard to press buttons "simultaneously." E.g. if the user wants to "move down" (1+2), they're either going to press (1) "move left" first, or they're going to press (2) "rotate anti-clockwise" first. It gets even worse when the user has to press three buttons "simultaneously." If it was me in your position, I would ask the instructor whether I should be worried about that or not. \$\endgroup\$ Mar 1 at 20:40
  • \$\begingroup\$ six-core wire is misleading ... it means one conductor made of six wires ... you are referring to six conductor cable \$\endgroup\$
    – jsotola
    Mar 1 at 22:16
  • \$\begingroup\$ Difficult to compare truth tables when mapping is different. \$\endgroup\$ Mar 2 at 9:54

2 Answers 2

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It looks like the question author has forgotten to provide a mapping from A,B,C,D to 1,2,3,4. Therefor I would just pick a assignment arbitrarily and state it clearly. A=1, B=2 etc would be the most intuitive and is probably what the author intended.

Once that's resolved, taking a quick look at your truth tables.. I see that you've ordered the entries differently. I would recommend counting up from 0-15 with your inputs-as-a-binary-number, just for clarity (your second table), but it doesn't actually matter. That appears to be the only difference, besides the 1-4, a-d mapping?

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I would take your first truth table and switch it to read (d, c, b, a) and (4, 3, 2, 1) from left to right. Then use the same order of values. Since A is least significant digit it should be on the right, and it makes sense to keep the order and values from Figure 1 (0001 = only button 1 pressed). But it is pretty much semantics and if no format is specified you can't really go wrong.

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    \$\begingroup\$ Thanks, I've now included the truth table that I believe you mean. I do wish they specified the specific format as I've to now create sum-of-minterms expressions and then simplify one using boolean algebra and k-map. \$\endgroup\$
    – r4561226
    Mar 1 at 23:11

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