using the Zilog Z8 encore for the ultrasonic distance calculation.

research speed of ultrasonic wave.
figure out what resolution you want in your distance measurement.
research the accuracy of the ultrasonic transducer you have.

use the formulas gained in your research to calculate the minimum
period you want to count.  Set your timer to this period.

reset timer
pulse sonar
start timer

wait 4 echo
when echo is received, stop timer.

you need to scale time to distance,
and then you know how far away the echo
came from.

it is more "complicated" than this, but not
difficult to understand.  When you get an echo,
it could have come from any spot on a 45degree
circle segment.  The degree it came from may
vary with the transducer you use.

because sonar spreads out as it travels, the farther
away the echo came from, the wider area it could
have come from.

in your code your need to take this into account
if you want to be able to do anything useful with
the sonar data (in my experience)

Rich

Thank you Rich for all the inputs...its definitely a great
encouragement for the beginners like me.
-Priti