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Circuit Description

A very simple traffic light controller, realized as a Moore-type state-machine with two flipflops and a few gates. (Click the clock and nreset switches, or type the 'c' and 'r' bindkeys).

The state table looks like follows:

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

 z1* = (z1 & |z0) | (!z1 & z0)
 z0* = !z0

 led_red    = !z1
 led_yellow = z0
 led_green  = (z1 & !z0)