Interruption pins

Projects General Guidance
1

Hi,

I am using Arduino ATMega (1280) and I would like to confirm if I am really in trouble... Or there is no way to solve this issue?

  • I need an interruption pin to wake-up the processor.

  • I am already using INT0 and INT1 (pins Digital 2 and 3) as interruption pins to wake-up the MCU(working fine).

  • I am using the I2C bus, so INT3 and INT4 (pins Digital 21-SCL and 20-SDA) cannot be used. There are more than one device on this bus and I do not want (I am afraid of...) to include a hardware line on it to serve as an interruption pin...

  • Serial1 interface is being used (actually, I am using all 4 serial interfaces). therefore, INT4 (RX1) and INT5 (TX1) cannot be used.

thanks

2

Search for "pin change interrupt".

3

Or use diodes, like here:
Any of cathodes going low causes a low interrupt on the common anode, which is an input with internal pullup resister enabled.

4

Thanks for the replies!

The diode idea is very good and it is definitely an option for me.
While waiting for the replies, I had an idea. I am using one of the serial ports (Serial3) for a serial LCD.
Therefore, I can swap Serial1 with Serial3. In this way, the RX1 pin will be available (LCD only receives data) and I can use this pin for this purpose.

Question:
If I am using Serial1 (say, Serial1.begin(9600), etc...) for a serial LCD, can I still use the RX1 pin for interruption purposes or it compromised in someway with the serial library?

Thanks.

5

Re: Serial1 - I don't think so, unless you use Serial1.end, and then pinMode to set the pin to an input, and then Serial1.begin again later to turn it back on.
Otherwise I would expect your signal will likely just be seen as a start bit and fill the hardware buffer byte with 0s or 1s.

6

If you want to get an interrupt when you get serial data you can run a wire from the Rx pin to another interrupt pin. But you can't use Rx to handle a separate interrupting input. As CR says, the UART will have a hernia.

What is this other interrupt source, and why would it need to share the Rx pin?

Rob

7

Let me explain better the idea of using Serial1 and let me know if it will work...

  • The external interrupt pin INT4 shares the same pin as RX1 (the receive line of Serial1)

  • Serial1 is being used for LCD only; therefore, TX1 pin is being used but RX1 is not used at all; in other words, in the code I never read from Serial1

  • When sleeping, the Serial1 is not being used; in fact, before going to sleep, I shutdown many hardware pins and I also use Serialx.end()

  • Therefore, I believe that I can use INT4 (same pin as RX1) to wake-up the MCU

Comments?

8

I think that would work, won't know for sure until you try. Do the
serial1.end,
pinmode(RXpin, INPUT)
digitalWrite(RXpin, HIGH)
attachInterrupt(whatever it is, LOW),
etc.

Another thought:

Interrupts 6 & 7 do not seem to have been broken out, physical pins 8 & 9.

Perhaps solder little wires on and bring those to a connector.
Update the pins_arduino.c so the software can use them.

That's what we really need - a software tool to let you select a processor, define the mapping you want the pins to have to real hardware, and let it create custom pins_arduino.c files. This is the 3rd time this month where that would have been handy now...

9

Interrupts 6 & 7 do not seem to have been broken out,

And that's a mind-boggling design decision in itself. The two pins are unconnected, just waving in the breeze.

I would also say you can use the Rx pin as you describe.

Rob