Question

Consider the following sequential circuit, which has no external inputs. REG3 is a 3-bit register. REG3 DO 00 00 DI 01 Q1 XORZ AND2 D2 02 Q2 XORZ clk clock

The following is an equivalent way of creating the circuit above.

Below is the truth table

Q2, Q1, and Q0 are LED outputs from left to right respectively and D2, D1, and D0 are switches from left to right respectively

Answer the following questions:

1. What signal(s) represent the present state and next state of the circuit?

2. Sketch a Finite State Machine diagram of the circuit (Be sure to show inputs and outputs).

3. Describe the high-level behavior of the circuit (what does it do?)

4. Given the function of the circuit, what does the state of the circuit represent?

Answer 1

Answer 1:

the signals that represent the present state.

(these are those signals which give the output of flip flop at the current clock cycle)

hence, Q0,Q1,Q2 are present state variables.

the next state variables are:

the variables that define what will be the next state of the FSM. when the next clock pulse arrives.

hence next state variables are D0,D1,D2

answer 2.)

outputs are given in state since its a moore machine. 000 111 there are no inputs except the clock. 001 110 101 010 100 011

answer 3:

the circuit has an output taken from

Q2,Q1,Q0.

from the table given and the state diagram we see that the value is binary is counting up. until it reaches 111 and then reverts back to 0 every time a clock pulse arrives.

hence the circuit is counting clock pulses. hence the circuit is an 3 bit Synchronous up counter.

answer 4:

the current state of the above circuit represents the number of clock cycles which has passed or supplied to the circuit in range from 0-7.

counting up.

hence the circuit is called an up counter.