C programming: bit vs. U8

Status
Not open for further replies.
C

CroneA

New Member
Hello everyone! I have a programming question regarding the use of C for a 8051 microcontroller.

I have been going over some Silicon Labs premade examples, it seems that for even a simple one bit variable they will declare it as a U8. Would there be a good reason why they aren't using the BIT data type?

Thanks!
 
Normally a structure would be created with bit patterns so you create a bit variable.

Look at this example... It comes from XC compiler on the PIC but it is ANSI C so will work on any compiler

C: 
// Register: INTCON
extern volatile unsigned char           INTCON              @ 0x00B;
#ifndef _LIB_BUILD
asm("INTCON equ 0Bh");
#endif
// bitfield definitions
typedef union {
    struct {
        unsigned IOCIF                  :1;
        unsigned INTF                   :1;
        unsigned TMR0IF                 :1;
        unsigned IOCIE                  :1;
        unsigned INTE                   :1;
        unsigned TMR0IE                 :1;
        unsigned PEIE                   :1;
        unsigned GIE                    :1;
    };
    struct {
        unsigned                        :2;
        unsigned T0IF                   :1;
        unsigned                        :2;
        unsigned T0IE                   :1;
    };
} INTCONbits_t;

Now you can access any of the bits within the declare SFR INTCON.

SDCC has its own way
C: 
__sbit __at 0xA0 pwm;
__sbit __at 0xA1 pwmn;
__sbit __at 0xA2 enable;

Remember that there are only a few DATA locations that accept bit access...
 
Generally c does not have a native bit type. Many programmer will use a byte aka U8 type which wastes 7 bits but makes accessing the variable faster then using just a bit and having to access a structure to get to it.
 
Status
Not open for further replies.

Similar threads

  • Article
89C51 environment build, ask for help.
Replies
2
Views
4K
MianQi
K
4-bit mode of LCD-1602 using 8052 µc
Replies
1
Views
6K
Ian Rogers
Expansion Board 8051 Core System Board Single Chip Microcomputer
Replies
0
Views
6K
nikson93
D
  • Question
Chinese Prechin PZ51 tracker
Replies
2
Views
5K
Dan Kwon
D
F
problem to understand how to divide two 16 bits number in 8051 microcontroller
Replies
1
Views
10K
rjenkinsgb
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…