EE 308 Setting and Clearing Bits

EE 308

Setting and Clearing Bits
using Assembly and C

To put a specific number into a memory location or register (e.g., to put 0x55 into PORTA):
```
ldaa    #$55            PORTA = 0x55;
staa    PORTA
```
To set a particular bit of a register (e.g., set Bit 3 of PORTA) while leaving the other bits unchanged:
```
bset    PORTA,#$10      PORTA = PORTA | 0x10;
```
To clear a particular bit of a register (e.g., clear Bit 4 of PORTA) while leaving the other bits unchanged:
```
bclr    PORTA,#$20      PORTA = PORTA & 0xDF;

                        PORTA = PORTA & ~0x20;
```

Bill Rison
2000-02-11