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We suggest that you go to
the DIGITAL INDEX and
read the pages on DECADE
COUNTERS and BINARY TO 7
SEGMENT DECODERS before
reading this.
The oscillator is
crystal controlled to
give a stable frequency.
A high frequency is used
to keep the size of the
crystal small.
The divide by 250 gives
an output of 128 pulses
per second.
These are fed to the
first counter/divider
which divides by 128 to
give a pulse every
second.
It counts these pulses,
in binary, up to 59
seconds.
The count is shown on
the first 7 segment
display.
Since the output from
the counter is in binary
form, it is converted to
suit the display by the
decoder.
When the count and
display reaches 59
seconds, it resets to
zero on the next pulse.
The one second pulses
are also sent to the
next divider/counter
which divides by 60 to
give one pulse every
minute.
These pulses are counted
and displayed as
minutes.
When the count and
display reaches 59
minutes and 59 seconds
it resets to zero on the
next pulse.
A pulse every minute is
fed to the final
divider/counter.
This divides by 60 to
give one pulse every
hour.
These pulses are counted
and displayed as hours.
When the count and
display reaches 23 hours
59 minutes 59 seconds,
the counters and display
resets to zero on the
next pulse. |
