topic Structure bit field in S12 / MagniV Microcontrollers

Structure bit field

Aswin_5232 — Wed, 25 Mar 2026 09:23:25 GMT

Hi, I am using CodeWarrior 5.2 and the controller is MC9S12DG256B.

When I am assigning each structure element with values and finally reading the overall value using union it is giving different values. how to solve this issue. I think there is difference in byte ordering.

typedef union

{

unsigned long w;

struct {

unsigned long disp_comp_cal : 2;//0

unsigned long disp_home : 2;//2

unsigned long disp_trips : 2;//4

unsigned long disp_fuel : 2;//6

unsigned long disp_hours : 2;//8

unsigned long disp_service : 2;//10

unsigned long disp_diags : 2;//12

unsigned long disp_slftst : 2;//14

unsigned long disp_cust_set : 2;//16

}b;

}attrib2;

Re: Structure bit field

lama — Thu, 26 Mar 2026 09:02:52 GMT

Hi,

look into attached file to see solution.

You should think about compiler setup .... look into the help or manuals ... keyword=bitfield.

Your issue is order of bits in the bitfield.

Best regards,

Ladislav

My test code:

#include "derivative.h" /* derivative-specific definitions */

//******************************************************************************

typedef union

{

unsigned long w;

struct

{

unsigned char disp_comp_cal : 2;//0

unsigned char disp_home : 2;//2

unsigned char disp_trips : 2;//4

unsigned char disp_fuel : 2;//6

unsigned char disp_hours : 2;//8

unsigned char disp_service : 2;//10

unsigned char disp_diags : 2;//12

unsigned char disp_slftst : 2;//14

unsigned char disp_cust_set : 2;//16

unsigned int dummy : 14;

}b;

}attrib2;

//******************************************************************************

void main(void)

{

attrib2 attrib22;

attrib22.w = 0x00UL;

attrib22.b.disp_comp_cal =2;

attrib22.b.disp_home =1;

attrib22.b.disp_trips =3;

attrib22.b.disp_fuel =1;

attrib22.b.disp_hours =2;

attrib22.b.disp_service =1;

attrib22.b.disp_diags =3;

attrib22.b.disp_slftst =1;

attrib22.b.disp_cust_set =1;

attrib22.b.dummy =0x3FFFF;

// expected 0B1001 1101 1001 1101 0111 1111 1111 1111

// 0x9D9D 7FFF

DDRAB = 0xFFFF;

//------------------------

for(;;)

{

attrib22.b.disp_comp_cal +=1;

attrib22.b.disp_home +=1;

attrib22.b.disp_trips +=1;

attrib22.b.disp_fuel +=1;

attrib22.b.disp_hours +=1;

attrib22.b.disp_service +=1;

attrib22.b.disp_diags +=1;

attrib22.b.disp_slftst +=1;

attrib22.b.disp_cust_set +=1;

PORTAB = (unsigned int) (attrib22.w & 0xFFFFUL);

PORTAB = (unsigned int) ((attrib22.w >> 16) & 0xFFFFUL);

}

//------------------------

EnableInterrupts;

//------------------------

for(;;)

{

_FEED_COP(); /* feeds the dog */

}

//------------------------

}

//******************************************************************************

Re: Structure bit field

Aswin_5232 — Thu, 26 Mar 2026 10:40:28 GMT

Hi Lama,

Thanks it is working now.

Re: Structure bit field

Aswin_5232 — Mon, 06 Apr 2026 06:27:37 GMT

Hi Lama, when I am changing the project settings this issue get resolved but values read from different PORTS are also getting reversed. Any other solution for this.