Tracy Smith says
Here are a couple of ideas for getting 1<<TestBit10 cycles: 2^n: clrw btfsc TestBit,2 movlw b'11111100' addwf TestBit,f incf TestBit,w btfsc TestBit,1 iorwf TestBit,f incf TestBit,f skpnc swapf TestBit,f ......... another way (7 cycles [including the call]) two_to_n: andlw 7 addwf pcl,f retlw 1 retlw 2 retlw 4 retlw 8 retlw 0x10 retlw 0x20 retlw 0x40 retlw 0x80 ............ or probably more to the point movf portb,w movwf portb_shadow btfss TestBit,2 swapf portb_swadow,f btfss TestBit,0 rlf portb_shadow,f movlw b'10000000' btfss TestBit,1 movlw b'00100000' andwf portb_shadow,f skpnz goto _the_bit_is_set .lo
Kevin Blain says:
clrf mask ; empty the mask ; a file called bit contains the 0 to 7 value of the bit position incf bit ; make it 1 to 8, so decfsz works nicely bsf STATUS, C ; set the carry flag. This will be rotated in 'bit' times loop: rlf mask, f decfsz bit, f ; skip out after 'bit' times. goto loop ..... ; rest of code... Of course, it would be good to ensure that bit is not greater than 7 when entering the routine.
Scott Dattalo says
set_bit: ;Get a pointer to the byte containing the bit we want: rrf bit_position,w movwf fsr rrf fsr,f rrf fsr,w andlw BIT_ARRAY_MASK addlw bit_array movwf fsr ; find 1<<(bit_position&7) [note, this could be made 2-cycles ; shorter] movlw 0101b btfsc bit_position,0 movlw 1010b movwf mask movlw 0011b btfsc bit_position,1 movlw 1100b andwf mask,f btfsc bit_position,2 swapf mask,f ; now set or clear the bit movf mask,w iorwf indf,f ; Assume we're setting. btfss new_state,0 xorwf indf,w ; assumption was wrong
;Probably it would be better to pre allocate bit position value in cell ;shifted by one bit to left, like xxxx.yyyz where xxxx is byte offset ;and yyy bit offset. It let us write more tight code for this case. set_bit: swapf bit_position,W andlw 0x0F addlw bit_array movwf FSR movlw 1 btfsc bit_position,2 ;y.1 movlw 4 movwf mask btfsc bit_position,1 ;y.0 addwf mask,F btfsc bit_position,3 ;y.2 swapf mask,F movfw mask iorwf INDF,F btfss bit_position,0 ;we can use z for this why not? xorwf INDF,F
Bob Ammerman says:
To turn on bit "BitNum" of port "PortNum": movf PortNum,W movwf FSR movf BitNum,W call BitToMask iorwf INDF,F To turn off bit "BitNum" of port "PortNum": movf PortNum,W movwf FSR movf BitNum,W call BitToMask xorlw 0xFF andwf INDF,F ; To test bit "BitNum" or port "PortNum" movf PortNum,W movwf FSR movf BitNum,W call BitToMask andwf INDF,W ; At this point Z is set if PortNum,BitNum was clear ; Z is clear if PortNum,BitNum was set BitToMask: addwf pcl retlw 1 retlw 2 retlw 4 retlw 8 retlw 16 retlw 32 retlw 64 retlw 128
; 2003-06-10T09:01:22Z ; test bit #n of working register, Z flag set properly, W left with bit btfsc n,0 andlw 0xaa btfss n,0 andlw 0x55 btfsc n,1 andlw 0xcc btfss n,1 andlw 0x33 btfsc n,2 andlw 0xf0 btfss n,2 andlw 0x0f+
|file: /Techref/microchip/math/bit/setbit.htm, 5KB, , updated: 2003/6/10 12:58, local time: 2020/8/10 23:09,
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