I haven't paid attention to power reset until now because I've been focusing
on software.
I'm currently supplying power through the motherboard connector (external
connector), but noticed that I was having a bit of trouble with the reset
button not always resetting the processor board. So I started looking at
reset by powering off the power supply. I noticed that by powering the board
through the external connector that the reset circuitry wasn't resetting the
board. It does if I remove the board from the mother board.
Using a scope I can verify that the reset chip produces a 250 ms pulse on
power up.
My power supply drives the 5 volt regulator, which in turn drives the 3 volt
regulator. With the scope I can verify that the 3 volt is regulating before
the 5 volts is regulating.
The mother board contains 74hc245 drivers to isolate my other hardware from
the CPU bus, and a MOSFET transistor takes the SA_NRESET line to the rest of
my hardware.
I noticed that if I hold the reset button down for several seconds that most
of the time I can get the cpu board to reset. There has been an occasion
that it hasn't. With the scope this shows the reset pulse being extended.
It seems that something is not starting within the 250 ms alloted for reset.
Can someone give me some clues as to whats going on here?
--Glen
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