Traffic light controller (2/4)

Description

Another traffic light controller. (Click the clock and nreset switches, or type the 'c' and 'r' bindkeys).

In this example, the state-encoding is chosen so that each flipflop directly encodes one output: flipflop z0 drives the red LED, z1 the yellow LED, and z2 the green LED. Therefore, no additional gates are required for the 'lambda' circuit of the Moore model. However, one additional flipflop and a more complex 'delta' circuit are required in comparison the realization demonstrated in the previous applet.

Over the years, many different and elaborate algorithms have been proposed to automatically find good solutions to the state-encoding and logic-minimization problems. Note that the quality of a solution largely depends on technological constraints like implementation technology (bipolar, CMOS), architecture (full-custom, FPGA), required clock-frequency, power-consumption, etc.

state       encoding   next state
            z2 z1 z0   z2* z1* z0*
----------------------------------
reset        0  0  0     0   0   1
red          0  0  1     0   1   1
red+yellow   0  1  1     1   0   0
green        1  0  0     0   1   0
yellow       0  1  0     0   0   1

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