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ADSP-21469 EZ Board Schematic Abnormality

Question asked by Alcor on May 7, 2010
Latest reply on Jun 8, 2010 by CKPATEL

There is a kind of abnormal work with the EZ-Board. I am trying to toggle the board LEDs in the timer0 interrupt routine. The pulse duration, measured on a LED with an oscilloscope should be 50%. But in fact it is not so. This is clearly seen at small blinking periods, e.g. 1 uS. The pulse width at 1 uS is about 25% instead of 50%. At 0.1 uS the LEDs often do not toggle at all. When I tried to check the input signal on the input of U17 it turned out, that the signal waveform is NOT rectangular. In fact it is almost linear sawtooth pulse of correct duration. It looks as if the output of the DSP is overloaded with too large capacitive load.

 

What is the explanation and is there any workaround? I need to observe small time intervals for debugging.

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