PORTB is a register value for each of (1-7)? digital_io. It says what each bit is in the datasheet, I would suggest taking a look at that.
basically
Code:
Port_B_Delta = Port_B ^ Old_Port_B; // determine which bits have changed
that line uses the XOR to compare the new value to the old one. so if you have 10010101 as your old one and 10000101 as your new one the "Port_B_Delta" will be 00010000 which is also = 0x10 in hex and = 16 in our regular number system.
which is where this comes into play:
Code:
if(Port_B_Delta & 0x10) // did external interrupt 3 change state?
{
or something like that...