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: 2019/6/25 00:41,
|©2019 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.massmind.org/techref/microchip/math/bit/setbit.htm"> Setting bit number X</A>
|Did you find what you needed?|
Welcome to massmind.org!
Welcome to www.massmind.org!