Re: External interrupt

On 25 Mar 2007 20:07:13 -0700, "galapogos" <goister@xxxxxxxxx> wrote:

Hi,

I have a MCU project on a Toshiba MCU that only has 1 pin for external
interrupt. However, I need 2 external interrupts from 2 devices. I'm
wondering if there's a way to share that 1 pin between the 2 external
interrupt inputs? I'm thinking of wiring the MCU pin directly to the
inputs from the 2 devices A & B, and also wire those 2 devices to 2
other GPIO pins(say pin A and B). Then in my ISR, I can perform a
check to see if pin A or pin B is high/low in order to determine which
device caused the interrupt. Of course there will be priority given to
either A or B. Will wiring both devices to the single MCU pin be a
problem? I'm guessing I'll need a pull up/down just in case, but I'm
also wondering if device A driving the pin will cause any weird
behavior on device B, since they're essentially connected together.

For low level active interrupts, your system will work if you put a
diode in series with both interrupt pins, cathodes conneted to int
pins, anode connected together, and also to a pull-up resistor, and
also to MCU interrupt input pin.

Use schottky diodes preferably

Zara


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