Because the infrared sensor is sensitive to the environment,
we need to filter out the transient noise by a digital filter. To
avoid the transient noise, the digital filter consists of a SR
flip-flop and three D flip-flops to synthesize the noise-elimination
circuit. The A/D converter control module consists of an
up-counter, a digital filter, and a delay circuit. The up-counter
generates the “WR” signal to start the A/D converter, then
the analog signals of the six infrared sensors are converted to
six 8-bit digital signals. After the digital filter, the distance
information is figured out, and then the module produces the
enable clock of the behavior selection control module to read
these signals. The delay circuit is mainly used to determine
how much time the CLMR should stay at the parking lot.