S4-P2 Flashcards
2
A
Note: Put the selectors in one side in k-map, for example if it were xz instead of xy, you must put xz together in the k-map since we need them together to find the required gates.
- for xy=00, we use 0 for don’t care, and I0 would be 0 at all times.
- for xy=01, to determine the input for I1, we use ~t since they can return 1 (here we use don’t care =1)
- for the other two, we just put 1 for I2, I3
- To create ~t we can use a NAND or a NOR
Important Notes
4
A
Note: If no current pass the the resistor, it means both ends of it have the same voltage.
2
A
Note: We write the truth table based on the Enable input of the Decoder for ease of calculation.
2
A
Note On Forbidden Inputs: If some inputs cause contention (Contention in logic circuits refers to a situation where two or more devices or components try to drive the same signal or bus at the same time) it’s a forbidden input and the output is don’t care. Or if the input to a gate is HZ, it’s also forbidden.
For example, When a and c are both 0, the buffers won’t transfer anything an their outputs are HZ and For abc=101, we’d have contention and hence, don’t care.
Note: A K-map is easier.
4
A
Note On BCD: The MSB is the place value of 10, meaning that if we have 15 as input, its BCD would be 1 0101, the first 1 is th MSB with place value of 10.
Note On DeMux: chooses the output based on the selector.
Note One XNOR: If the number of 1s is even, returns 1.
End Of P2
