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Traffic light controller (4/4, ROM-based)

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Circuit Description

Yet another traffic light controller, realized as a Moore-type state-machine. This time, however, both the next-state encoding as well as the output data are stored in a ROM addressed by the current state (via the flipflop outputs) and three switches that control the traffic light behaviour:

  • Blink: Selects a blink-only mode.
  • TG: Selects a longer green-phase (6 instead of 3 clocks)
  • TR: Selects a longer red-phase (6 instead of 3 clocks)
The bindkeys 'b', 'g', and 't' are used for the blink, long-green, and long-red switches, with 'r' and 'c' use for the nreset switch and the clock generator.

Use edit-component command from the popup-menu to open the memory editor and view the ROM contents. Note that both the next-state output (four bits) and the LED output values (three bits) fit into one word of the 1Kx8 bit ROM. Obviously, using a ROM of size 1Kx8 bits is wasteful, a ROM of size 128x8 bit would have been sufficient to store the traffic-light data in this example.

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Impressum http://tams.informatik.uni-hamburg.de/applets/hades/webdemos/18-fsm/10-trafficlight/ampel_43.html