newbie Q: Overlaying structs on ports

[cwatters]

Can I check that I've understood this right... Is it possible to twiddle individual output pins in a port by twiddling the corresponding bit in an overlay struct as follows....

struct port_b_layout {
int digit_en0 : 1;
int digit_en1 : 1;
int digit_en2 : 1;
int digit_en3 : 1;
int digit_en4 : 1;
int digit_en5 : 1;
int digit_en6 : 1;
int digit_en7 : 1;
};
struct port_b_layout port_b;
#byte port_b = 6

..and later in main loop

set_tris_b(0); //all outputs
port_b.digit_en0=1 //toggle pin digit_en0=RB0
delay_us(25)
port_b.digit_en0=0
delay_us(25)

[Mark]

Yep

[Jim Hearne]

I would have done it like this, it's even simpler and doesn't need the struct.

#byte port_b = 6
#bit digit_en0 =port_b.0
#bit digit_en1 =port_b.1
#bit digit_en2 =port_b.2
#bit digit_en3 =port_b.3
#bit digit_en4 =port_b.4
#bit digit_en5 =port_b.5
#bit digit_en6 =port_b.6
#bit digit_en7 =port_b.7


..and later in main loop

set_tris_b(0); //all outputs
digit_en0=1 //toggle pin digit_en0=RB0
delay_us(25)
digit_en0=0
delay_us(25)

[burnsy]

Yeah, but some of us just LOVE to use structures ;) It doesn't make much difference but I would have laid it out like this..

defines somewhere......
#define RESET = 0
#define IS_RESET == 0
#define SET = 1
#define IS_SET != 0

then the structure.....

struct {
char sw0 : 1;
char sw1 : 1;
char sw2 : 1;
char sw3 : 1;
char sw4 : 1;
char sw5 : 1;
char lamp1 : 1;
char lamp2 : 1;
}port_b, tris_b;

#byte port_b = 0x06
#byte tris_b = 0x86


In the code...

if (port_b.sw1 IS_RESET)
{
port_b.lamp1 SET; /* turns on lamp1 */
port_b.lamp2 RESET; /* turns off lamp2 */
}

Careful when ever you are testing the structure as a whole with the IF statement. In my experience with PCM 3.058 this..

if (port_b == 42)

would produce strange results. If i did this..

x = port_b;
if (x == 42)

would produce what I expected in the first place??? not sure why but adding this line under the structure definition fixes it.

#define PORT_B_BITS (*((UCHAR*)(&port_b)))

if (PORT_B_BITS == 42)

Works like a charm, no increase in code size. Credit goes to my former employer for that line
_________________
This is the last code change until its ready....