[SI-LIST] Re: Strange resets happening in one of our circuit boards
- From: "Hill, John" <jhill@xxxxxxxxxx>
- To: <a.ingraham@xxxxxxxx>, "SI-List" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 6 Jun 2006 12:52:33 -0400
Hello,
I like to add a series 100 ohm resistor at the reset pin on the
microprocessor. With a 10K pull-up the voltage divider is not an issue,
but with a scope you can see what is going on.=20
This does two things. First, there is a little RC to the input. Second,
if there are multiple open collectors on the reset pin, you can tell
which pin is driving the reset signal low.=20
When you show a programmer that current is going into their chip, they
believe that it is really his chip pulling the reset low.
Best regards,
John
=20
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Andrew Ingraham
Sent: Friday, June 02, 2006 11:43 PM
To: SI-List
Subject: [SI-LIST] Re: Strange resets happening in one of our circuit
boards
> Even though reset durations may be long, you still need to bring
> everybody out of reset in a timely fashion.
...
> Thus the asserting edge of reset might be slow, but the negating
> edge may need to be faster.
And in other cases the asserting edge needs to be reasonably fast too.
Sometimes it's necessary to "get everyone off the bus" (disable all
output
buffers) quickly. "Quickly" here may mean on the order of 10s of
nanoseconds; not exactly lightning fast, but not so slow that you don't
care
either.
The designer needs to understand the system's requirements,
specifications,
and Reset timing. Each case may be different.
Regards,
Andy
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