What is minimum input current on interrupt pins?

Steel

I have a project.· My SX is expecting a pulse from another chip as an interrupt.· The chip sends the pulse, and I have an LED indicator showing the pulse is sent...

...But the SX chip is not seeing the pulse.

When I hook 5V to the interrupt pin, it acts as it should...but the SX doesn't seem to be seeing the pulse when it is sent from this chip...(about 20mA).

Are there voltage/current limits on interrupt pins?

thanks.
Shaun


Post Edited (Steel) : 9/22/2006 6:05:23 PM GMT

Mike Green

How are you connecting the LED? Interrupt pins take very very little current and use the same voltage thresholds as any other pin. Sometimes, when you have an LED on a chip's output, it pulls the voltage up or down (depending on how you've connected it) so that it's too high (or too low) to properly trigger the interrupt pin. Try decreasing the LED current (by increasing the value of the current limiting resistor). Many chips can only handle 10-20ma without the voltage going too high (or too low).

Bean

Shaun,
The input pins are triggered by voltage level, not by current.
Do you have the LED connected directly to the interrupt pin (or through a resistor) ?
If so, the LED is probably loading it down so it doesn't trigger the SX pin.
Interrupts follow the settings for threshold, so if you didn't change the pin it should interrupt when it crosses 1.4volts.
Possibly the pin is being held above that voltage at all times, that would cause it not to interrupt also.
Try putting a meter on the lead instead of the LED. That will load it down less.

Bean.

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Steel

Right now the LED is with a 330 ohm resistor. I am going to increase the resistor, and verify the logic levels. Thanks