Defining single bit variables in Microchip C18

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Nemesis77

Joined: 20 Feb 2009
Posts: 3
Location: South Africa

11 May 2009 10:56 bit z charu c18

I want to define flags in my code. In assembler I used to do it as follows:

flags equ 0x020 ; Define variable

#define flag0 flags,0 ; Flag0
#define flag1 flags,1 ; Flag0
etc.

How would I do this in C18. i.e. I want to define a CHAR variable and I want to be able to set or clear each bit of the 8bit CHAR variable. C18 has some predefined for example... INTCONbits.GIE = 1; This statement sets only 1 bit in the INTCON register.

btbass

Joined: 20 Jul 2001
Posts: 1267
Helped: 115
Location: Oberon

11 May 2009 17:49 c18 bits

You use bitfields.

Code:

/*--- Relay Structure ---*/

struct RELAYBITS
{
unsigned rca:1; /* SEL_UNBAL relay */
unsigned earth:1; /* EARTHSEL relay */
unsigned ground:1; /* GND_RLY relay */
unsigned phase:1; /* Phase invert relay */
unsigned bridge:1; /* Mono amplifier mode */
unsigned dummy:2; /* Alignment bits */
unsigned mute:1; /* MUTE relay */
};

/*--- Relay bits union ---*/

typedef union
{
struct RELAYBITS Bits;
unsigned char data;
}RELAY;

volatile RELAY RELAYbits;

You can set and clear the bits like this:

Code:

RELAYbits.data = 0; /* Clear all bits */

RELAYbits.Bits.ground = 0; /* Clear single bit */
RELAYbits.Bits.rca = 1; /* Set a bit */

Bit fields dont have to be single bits, you could define a bitfield with 3 bits, or any number of bits

Code:

typedef struct
{
unsigned threebits : 3;
unsigned twobits : 2;
}BITS,

volatile BITS Bits;

Bits.threebits = 7;
Bits.twobits = 3;

then you could set them to any value between 0 and the maximum value the bits can hold.