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Originally Posted by Andrew
There also appears to be an interrupt service routine for the low priority interrupt and which can be executed using the 6 digital input pins on the front of the EDU-RC, labelled "Interrupt."
This code would execute whenever a transition (low-to-high, I think) is initiated on one of those pins.
In embedded, interrupt driven code you have to give up the notion of step-by-step execution. Multiple programs can be running simultaneously and which interact with each other.
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Just to clarify on the interrupts.
There are a total of 8 input pins on the pic that trigger interrupts. In the low priority int handler routine they give us, we only have access to 6 of them, and since there are only 6 pins, I'm assuming they use int0 and int1 for other purposes.
4 of the 8 interrupt pins (B0-B3) interrupt on either a rising edge or a falling edge (not both), and you can select between the two using the appropriate INTCON. The other 4 (B4-B7) trigger an interrupt on change, rising or falling (both). There is only 1 flag assossiated with all 4 pins, so if the interrupt triggers you need to compare the current state of all 4 pins to the state before the interrupt to figure out which one changed.
I'm pretty sure pin 1 of the interrupts is connected to port B pin 2, pin 2 to port B pin 3, etc down the line, so the last 4 are the interrupt on change pins.