On Sat, 23 Apr 2011 10:00:51 -0700 (PDT), Jeroni Paul
wrote:

I have a Kaon satellite/terrestrial decoder that while starting up it
will reboot several times until it works. After a lot of checking and
testing it seems the front panel micro AT89S52 sometimes won't wait
long enough for all the hardware to initialize. Precise measurements
on the communications between this micro and the main video decoder
reveal that the hardware initializes always at the same speed and it
is the AT89S52 micro that sometimes waits longer and thus starts
successfully but sometimes aborts too early. I don't know what else to
check: supply 5V to the micro perfectly clean, even added capacitors
to check, clock clean (has its own 12MHz crystal). Don't know what
else to check, I can only conclude the micro is faulty. Unfortunately
I don't have the code that runs inside so I don't know if that delay
is implemented by a loop or a hardware timer.

Hold it in a reset state longer on startup. These guys are unusual in
that their RST pin is active high, so keep that in mind.

The naive way to implement reset in this family is just a cap to the
positive supply rail, a resistor to ground, and the RST pin in between.
If this is what they used, it sounds like you're just on the edge of
reliability and may be able to make it happy by boosting the RC time
constant a tad by using a larger C or R, depending on which is easier to
get to.

There are also "supervisory" chips that are more reliable and can also
take care to reset on brown-outs. Some of these hold reset active for a
fixed interval but, IIRC, some set the time with an external R or C.

--
Rich Webb Norfolk, VA