system
October 15, 2011, 8:24pm
1
Hello to every arduino fans.
I was trying to understand some line codes took from a nunchuck code i found on internet...
static void nunchuck_setpowerpins()
{
#define pwrpin PORTC3
#define gndpin PORTC2
DDRC |= _BV(pwrpin) | _BV(gndpin);
PORTC &=~ _BV(gndpin);
PORTC |= _BV(pwrpin);
delay(100);
}
They set the analog pin 2,3 of arduino as power and gnd for the protocol. My problem is understanding all of the assignment: what are the central lines saying? And to who? I tried to look in atmega datasheet but I didn't find anything: can anyone help me?
what are the central lines saying?
The are the inclusive OR operation
DDRC |=
This says make the register called DDRC equal to what is was and inclusive ORed with what follows.
Generally what you are doing is setting individual bit is a register or variable.
DDRC is the data direction register of port C, it defines what bits of the port are inputs and which are outputs.
MarkT
October 15, 2011, 10:24pm
3
That code will expand out to something like:
static void nunchuck_setpowerpins()
{
// #define pwrpin 3 - pwrpin mask is 0x08 (bit 3)
// #define gndpin 2 - gndpin mask is 0x04 (bit 2)
DDRC |= 0x0C ; // set both pins as OUTPUT
PORTC &= ~0x04 ; // force gndpin LOW
PORTC |= 0x08 ; // force pwrpin HIGH
delay(100);
}