LPC824 SCT misses input events

[remcopoelstra]

Hi,

I'm using the SCT to monitor a watchdog signal. The signal toggles at a rate of 10Hz.

I've defined two events. One for the rising edge and one for the falling edge. They both capture (and limit) the counter and they set (event 0) or clear (event 1) an output pin.

The LED connected to the output pin blinks very irregularly and when I enable interrupts on the events and inspect the captured value, I noticed that it's sometimes around 3e6, which boils down to 100ms (counter is running at 30MHz), while the events should occur every 50ms, again indicating a missed event.

I inspected the watchdog signal with a scope and it looks very clean.

What could be the cause of the missed events?

Thanks in advance.

Kind regards,

Remco Poelstra

[jeremyzhou · Accepted solution]

Hi  Remco Poelstra,

Thank you for your interest in NXP Semiconductor products and 

the opportunity to serve you.

To provide the fastest possible support, I'd highly recommend you to refer to the Deconding PWM demo in the AN11538 whose link is below.

cache.nxp.com/documents/application_note/AN11538.zip?fsrch=1&sr=6&pageNum=1

Have a great day,

TIC

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[remcopoelstra]

Hi,

Thanks for the document. It solved my problem, by drawing my attention to the INYSNC feature, which I had disabled by accident.

Kind regards,

Remco Poelstra