Multiple Hardware Interrupt signals

[Pariah_Zero]

My memory is fuzzy and my google-fu is failing me

I've been working on a design with a number of chips are connecting to a microcontroller using i2c.

A bunch of the chips have open drain interrupts, so it's easy to chain them to the same pin on the MCU, and then query the chips when an interrupt is received...

However, one of the chips has four interrupts which are logic level pins (not open drain); as I recall these can't be simply chained together, as I'd end up with one chip fighting to hold the interrupt high, while the others fight to hold it low, with an eventual release of blue smoke.

There are only a few external interrupt pins; certainly more than I have available interrupt pins.

So what options are available to handle more interrupts than available interrupt pins?

[TerraHertz]

The magic words are 'Programmable Interrupt Controller'. PIC.

Read up on the old x86 legacy chips like the 8259. Maybe there's something equivalent today.
Or, use a small programmable logic device to implement a simple PIC.

[AlfBaz]

There's always the 74LS32 

[dannyf]

So what options are available to handle more interrupts than available interrupt pins?

Using diodes to OR them.

[qno]

You can use a transistor with a pull up resistor.

To quicky see the device that made the interrupt use a decimal to hex demultiplexer.

checkout 74xxx147

[NiHaoMike]

You could use diodes if they're active low or a transistor and resistor if they're active high.

Another solution is to use a PCF8574 or similar, but that's probably more complex than necessary.

[dannyf]

a transistor and resistor if they're active high.

Diodes can OR them if they are active high too.

[NiHaoMike]

a transistor and resistor if they're active high.

Diodes can OR them if they are active high too.

You'll still need to invert it to connect it to an active low bus.

[dannyf]

No.

[NiHaoMike]

No.

He already has an active low interrupt bus. Using another I/O to make an active high interrupt bus is one option, but if I/Os are scarce, a better choice might be to use a transistor and two resistors to tie it into the active low bus. (The second resistor is to pull down the line when no interrupt is active. Otherwise, the line will float when there's no interrupt and be prone to noise.)

[dannyf]

...

Diodes can OR active high signals or active low signals.