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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)

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.