module svaletlb 
title 'Output-Coded State Machine for Sunnyvale Traffic Lights' 
"SVALETLB device 'P16V8R'; 

" Input and output pins 
CLOCK, !OE                           pin 1, 11; 
NSCAR, EWCAR, TMSHORT, TMLONG        pin 2, 3, 8, 9;
NSRED, NSYELLOW, NSGREEN             pin 19, 18, 17 istype 'reg'; 
EWRED, EWYELLOW, EWGREEN             pin 16, 15, 14 istype 'reg'; 
TMRESET_L, XTRA                      pin 13, 12 istype 'reg';

" Definitions 
LSTATE  = [NSRED,NSYELLOW,NSGREEN,EWRED,EWYELLOW,EWGREEN,XTRA]; " State vars
NSGO    = [    0,       0,      1,    1,       0,      0,   0]; " States 
NSWAIT  = [    0,       1,      0,    1,       0,      0,   0]; 
NSWAIT2 = [    0,       1,      0,    1,       0,      0,   1]; 
NSDELAY = [    1,       0,      0,    1,       0,      0,   0]; 
EWGO    = [    1,       0,      0,    0,       0,      1,   0]; 
EWWAIT  = [    1,       0,      0,    0,       1,      0,   0]; 
EWWAIT2 = [    1,       0,      0,    0,       1,      0,   1]; 
EWDELAY = [    1,       0,      0,    1,       0,      0,   1];

state_diagram LSTATE 
state NSGO:                      " North-south green
   IF (!TMSHORT) THEN NSGO       " Minimum green is 5 seconds.
   ELSE IF (TMLONG) THEN NSWAIT  " Maximum green is 5 minutes.
   ELSE IF (EWCAR & !NSCAR)      " If E-W car is waiting and no one
          THEN NSGO              "  is coming N-S, make E-W wait!
   ELSE IF (EWCAR & NSCAR)       " Cars coming in both directions?
          THEN NSWAIT            " Thrash!
   ELSE IF (!NSCAR)              " Nobody coming N-S and not timed out?
          THEN NSGO              " Keep N-S green.
   ELSE NSWAIT;                  " Else let E-W have it.

state NSWAIT: GOTO NSWAIT2;      " Yellow light is on for two ticks for safety. 
state NSWAIT2: GOTO NSDELAY;     " (Drivers go 70 mph to catch this turkey green!)
state NSDELAY: GOTO EWGO;        " Red in both directions for added safety.

state EWGO: " East-west green; states defined analogous to N-S
   IF (!TMSHORT) THEN EWGO
   ELSE IF (TMLONG) THEN EWWAIT
   ELSE IF (NSCAR & !EWCAR) THEN EWGO
   ELSE IF (NSCAR & EWCAR) THEN EWWAIT
   ELSE IF (!EWCAR) THEN EWGO  ELSE EWWAIT;

state EWWAIT: GOTO EWWAIT2; 
state EWWAIT2: GOTO EWDELAY; 
state EWDELAY: GOTO NSGO;

equations

LSTATE.CLK = CLOCK;  TMRESET_L.CLK = CLOCK;

!TMRESET_L := (LSTATE == NSWAIT2)  " Reset the timer when going into
            + (LSTATE == EWWAIT2); "   state NSDELAY or state EWDELAY.

end svaletlb