Hello everybody
i have a question about GCC and CodeVision: How can i changing PORTX register in other place of program. as you know, normally we setting it at Main function inside DDRX rigester for example like this:
DDRB = 0x00; PORTB = 0x00;
but how do you change it at other place? and an another question:
is it wisely that we setting DDRX and PORTX rigester like this(also for example)?:
DDRB.0=0; PORTB.0=1;
but how do you change it at other place?
void foo(void) {
PORTB = 0x55;
}
int main(void) {
DDRB = 0xFF;
while (1) {
PORTB = 0xAA;
foo();
}
}
then the PORTB output toggles between 0x55 and 0xAA. Does foo() count as "another place"?
is it wisely that we setting DDRX and PORTX rigester like this(also for example)?:
DDRB &= ~(1<<0); PORTB |= (1<<1);
which will work in any C compiler on earth (as long as "DDRB"/"PORTB" is known) or you can create a construct something like the CV feature with:
struct bits {
uint8_t b0:1, b1:1, b2:1, b3:1, b4:1, b5:1, b6:1, b7:1;
} __attribute__((__packed__));
#define MYPORTB (*((struct bits *)&PORTB))
int main(void) {
MYPORTB.b3 = 1;
true there has to be a 'b' there to make this into standard C but something like this should work in any C compiler.
Personally I like Peter Danegger's sbit.h solution for use with GCC - the above is based on that (I stole his bits{} structure).
Thanks Cliff
What do you mean "other place"?
DDRB = 0xff; PORTB = 0xff;
then the PORTB register put high logic at B pin/port.
when you set PORTX at main function like this:
DDRB = 0x00; PORTB = 0xff;
then the PORTB register put a pull-up resistor. thus, at main function, the PORTB register doesn't output or input toggles. correct?
but when we use the PORTB to other place like this(as you provided):
void foo(void) {
PORTB = 0x55;
}
int main(void) {
DDRB = 0xFF;
while (1) {
PORTB = 0xAA;
foo();
}
}
this register just does output or input and doesn't a high logic or pull-up resistor. my mean is this.
The AVR does not know where in your source code you do register manipulation. Thus, when you code e.g.
DDRB = 0xff; PORTB = 0xff;
or
DDRB = 0x00; PORTB = 0xff;
it does not matter if this is done in the main() function, or in some other function. The effects should be the same regardless of where in your code this is placed. Indeed, when the code executes from flash there are no significant traces left that indicates in which function the source code the instructions was generated from.
my mean is this.
Great Johan! thanks(especially for english language points)
but still i'm staggerer.
The effects should be the same regardless of where in your code this is placed.
PORTB = 0xff;
it set all B pin to output and when use of port like this(for example):
DDRB = 0xff;
it set all B pin to input.
really i confused. :?
ut i think when we use of these two register(DDRX or PORTX) in other place(except main function) they just set the port to output or input. i think when use of port like this(for example):PORTB = 0xff;it set all B pin to output
There is nothing special with where this is done, or in what order. Consider this example, and assume that DDRB and PORTB has not been touched since reset:
// Since both DDRB and PORTB is at their default value (i.e. 0) the port is set to input, and pull-ups are not enabled. PORTB = 0xFF; // The port is still set to input, but now the pull-ups are enabled DDRB = 0xFF; // The port is now set to output, and the pins are pulled high PORTB = 0x00; // The port is still set to output, but now the pins are pulled low DDRB = 0x00; // The port is set to input. Since PORTB is still 0x00 pull-ups are not enabled
Although I've manipulated all bits of the port, this is not necessary. You can of-course do similar operations on individual bits of the port.
All this is excellently documented in the data sheet, which you should read thoroughly until you understand it. For parts that you do not understand: Quite them here, or point to them, and we shall try to explain. For the meaning of DDRB and PORTB bits you should dlook in the section called "I/O Ports", and a table probably named "Port Pin Configurations". In the ATmega328P data sheet it is on page 78, and the table is numbered 14-1.
Well done, Johan! Thanks.
If you combine the bits of DDR and PORT then for each bit position (pin) there can only be four states:
DDR PORT 0 0 -- input floating 0 1 -- input with pull-up enabled 1 0 -- output driven low 1 1 -- output driven high
Well done, Johan! Thanks.
Thanks Cliff,
i already was confused, but now i understood it.
Thank you. Still, all I did was to flesh out the terse but precise table of the data sheet. You know what they say.. "When everything else fails, try reading the documentation." :wink:
Thanks Cliff,
i already was confused, but now i understood it.
Now, yes! :mrgreen:
