The following circuit is intended to be a gated latch circuit where the signal G

Question

The following circuit is intended to be a gated latch circuit where the signal G is
the gate.
(a) Derive the next-state equation for this circuit using Q as the state variable and
P as an output.
(b) Construct the state table and output table for the circuit. Circle the stable states
of the circuit.
(c) Are there any restrictions on the allowable input combinations on M and N?
Explain your answer.
(d) Is the output P usable as the complement of Q? Verify your answer.
(e) Assume that Gate 1 has a propagation delay of 30 ns and Gates 2, 3, and 4 have
propagation delays of 10 ns. Construct a timing diagram for the circuit for the
following input change:M N Q 0 with G changing from 1 to 0.

Explanation / Answer

1) A combinational Logic Circuit has 4 inputs ( A,B,C & D ) and One output Z . The output is iff the input has three consecutive Zeros or three consecutive ones . For example , If A=1, B=0 , c=0 and D=0 then Z=1 , but if A=0 , B=1 , C=0 and D=0 then Z=0
Design the circuit using one 4-input OR gate and 4 3-input AND gates .

2) Design a combinational logic circuit which has one output Z and a 4-bit input ABCD representing a binary number Z . Z should be 1 iff the input is at least 5 , but is no greater than 11 . Use one OR gate ( three inputs ) and three AND gates ( with no more than three inputs each ) .

3) A bank vault has three locks with a different key for each lock . Each Key is owned by a differefnt person . In order to open the door , at least two people must insert their keys into the assigned locks . The signal lines A,B,C are 1 if ther is a key inserted into lock 1,,2 or 3 respectively . write an equation for the variable Z which is 1 iff the door should open .
4

Sometimes really a state machine is implemented or programmed explicitely.
In many cases, nowadays a sequenced program is run (for instance on a microcontroller).

The := notation is decades old, you can find it for instance used in BCPL, or in PASCAL.

Is it true people really learn Karnaugh, CMOS, state machine, digital logic, and then later use it to produce a circuit or solution?

Or isn't it better first to examine a real world problem, and then see what could be used to implement it?

Or architecture, you can take some clay or LEGO or solder pieces of wires together and design some nice models of buildings. Don't care about maths or how to use some weird CAD software (i.E. to memorize the software menu's, and for instance answer questions about that on paper in a test).

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