The point I was making is that the Sony designers really skimped here in
their design. This set cost well over $2K and the clock gains about 3
minutes a month on the cheap oscillator they provided rendering the clock
pretty much completely useless. I have a $49 DVD player that synchronizes
it's clock from the local PBS so it is always accurate to the minute. I
have a $30 alarm clock that functions as James describes below using the AC
house current and with a backup oscillator for power loss. It just seems
Sony completely missed the boat here to save a dollar. It can't help but
make any intelligent consumer wonder where else they cut corners on their
top of the line set...

Bob

"James Sweet" wrote in message
news:5iG6e.15724$B12.6320@trnddc09...
Why doesn't it? I've used that feature on a microprocessor based clock I
built, it's just a matter of having code that synchronizes timekeeping to
the
AC line when present, and if that goes away it uses a timer interrupt driven
by the CPU's crystal oscillator. The benefit is rock solid long term
timekeeping (better than any crystal oscillator) when power is present
combined with backup that's reasonably accurate for short outages with no
added hardware other than a resistor and capacitor for the AC sync. I've
seen other designs that even autoselect between 50 and 60 Hz, again just
coding, no hardware change. Modern microcontrollers tend to have vast
amounts of memory for what they typically need, there's usually extra space
for cool features like this.

*Many* clock radios and other digital clocks use a very similar arrangement
though most of them use a simple R/C oscillator for the battery backup.