Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur télécharger pdf (Page 89)

Here,

tag

is an optional name of the structure;

bitfield-declarator-list

a list of bit fields. Each component identifer requires a colon and its width in bits

to be explicitly specified. Total width of all components cannot exceed one byte (8

bits).

As an object, bit fields structure takes one byte. Individual fields are packed with-

in byte from right to left. In

bitfield-declarator-list

, you can omit identi-

fier(s) to create artificial “padding”, thus skipping irrelevant bits.

For example, if we need to manipulate only bits 2–4 of a register as one block, we

could create a structure:

struct {

unsigned : 2,

// Skip bits 0 and 1, no identifier here

mybits : 3;

// Relevant bits 2, 3, and 4

// Bits 5, 6, and 7 are implicitly left out

} myreg;

Here is an example:

typedef struct {

prescaler : 2; timeronoff : 1; postscaler : 4;} mybitfield;

which declares structured type mybitfield containing three components:

prescaler (bits 0 and 1), timeronoff (bit 2), and postscaler (bits 3, 4, 5,

and 6).

Bit Fields Access

Bit fields can be accessed in same way as the structure members. Use direct and

indirect member selector (

. and ->). For example, we could work with our

previously declared mybitfield like this:

// Declare a bit field TimerControl:

mybitfield TimerControl;

void main() {

TimerControl.prescaler = 0;

TimerControl.timeronoff = 1;

TimerControl.postscaler = 3;

T2CON = TimerControl;

}

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Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur Page 89

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