S5704A Tips & Tricks 11 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 11 Tips and Tricks Tips and Tricks Using PICmicro ® MCUs

S5704A Tips & Tricks 12 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 12 Tips and Tricks Increments and Decrements 16-Bit Increment incfszLO goto$+2 incfHI 16-Bit Decrement decfLO incfszLO,W goto$+2 decfHI l 8-Bit Decrement to 0xFF NOT_AT_FF : decfREG incfszREG,W gotoNOT_AT_FF AT_FF: 16-Bit Increment incfszLO goto$+2 incfHI 16-Bit Decrement decfLO incfszLO,W goto$+2 decfHI l 8-Bit Decrement to 0xFF NOT_AT_FF : decfREG incfszREG,W gotoNOT_AT_FF AT_FF:

S5704A Tips & Tricks 13 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 13 Tips and Tricks ComparisonsComparisons 8-Bit Range Test Enter with value to be tested in W. Exits with Carry set if W is in the range [LOVAL to HIVAL], inclusive. addlw255-HIVAL addlw(HIVAL-LOVAL)+1 Compare and Swap Compare the values in registers X and Y. If Y = X? bc$+3;IF SO, JUMP AHEAD. addwfX;OTHERWISE, X = X + (Y-X) = Y, subwfY; AND Y = Y - (Y-X) = X. 8-Bit Range Test Enter with value to be tested in W. Exits with Carry set if W is in the range [LOVAL to HIVAL], inclusive. addlw255-HIVAL addlw(HIVAL-LOVAL)+1 Compare and Swap Compare the values in registers X and Y. If Y = X? bc$+3;IF SO, JUMP AHEAD. addwfX;OTHERWISE, X = X + (Y-X) = Y, subwfY; AND Y = Y - (Y-X) = X.

S5704A Tips & Tricks 14 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 14 Tips and Tricks ComparisonsComparisons Minimum Enter with three values stored in registers N1, N2, and N3. Exit with min(N1,N2,N3) in MIN, N1-3 unchanged, W scrambled. movfN1,w subwfN2,W movfN1,W skpc movfN2,W movwfMIN subwfN3,W skpc addwfMIN Minimum Enter with three values stored in registers N1, N2, and N3. Exit with min(N1,N2,N3) in MIN, N1-3 unchanged, W scrambled. movfN1,w subwfN2,W movfN1,W skpc movfN2,W movwfMIN subwfN3,W skpc addwfMIN

S5704A Tips & Tricks 15 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 15 Tips and Tricks Bit-ManipulationBit-Manipulation Reverse 7 Bits Enter with 0ABCDEFG in W. Exits with 0GFEDCBA in W. movwfsource ;source = 0ABCDEFG. swapfsource,w ;W= DEFG0ABC. btfscsource,3 ;If D = 1, invert D and the “0”. xorlw0x88 ;After this line, W = 0EFGDABC. btfscsource,6 ;If A = 1, invert bits A and C. xorlw0x05 ; btfscsource,4 ;If C = 1, invert A and C again. xorlw0x05 ;After this line, W = 0EFGDCBA. btfscsource,2 ;Do the same with E and G. xorlw0x50 ; btfscsource,0 ; xorlw0x50 ;After this line, W = 0GFEDCBA. Reverse 7 Bits Enter with 0ABCDEFG in W. Exits with 0GFEDCBA in W. movwfsource ;source = 0ABCDEFG. swapfsource,w ;W= DEFG0ABC. btfscsource,3 ;If D = 1, invert D and the “0”. xorlw0x88 ;After this line, W = 0EFGDABC. btfscsource,6 ;If A = 1, invert bits A and C. xorlw0x05 ; btfscsource,4 ;If C = 1, invert A and C again. xorlw0x05 ;After this line, W = 0EFGDCBA. btfscsource,2 ;Do the same with E and G. xorlw0x50 ; btfscsource,0 ; xorlw0x50 ;After this line, W = 0GFEDCBA.

S5704A Tips & Tricks 16 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 16 Tips and Tricks Bit-ManipulationBit-Manipulation Rotate in Place Rotate without inserting an extra bit from the carry. Easily extended to multi-bit rotates. Enter with ABCDEFGH in REG. Exits with BCDEFGHA in REG, W scrambled. rlfREG,W rlfREG Bit-Copy Copy bits from one register to the same position in another. movfSOURCE,W;The DEST bits in the positions to ;which we’re copying must not change xorwfDEST,W;between this xorwf instruction and ;the xorwf DEST below. andlw B;A "1" in each bit-position we’re ;copying.. ;this example copies the three LSBs. xorwfDEST Rotate in Place Rotate without inserting an extra bit from the carry. Easily extended to multi-bit rotates. Enter with ABCDEFGH in REG. Exits with BCDEFGHA in REG, W scrambled. rlfREG,W rlfREG Bit-Copy Copy bits from one register to the same position in another. movfSOURCE,W;The DEST bits in the positions to ;which we’re copying must not change xorwfDEST,W;between this xorwf instruction and ;the xorwf DEST below. andlw B;A "1" in each bit-position we’re ;copying.. ;this example copies the three LSBs. xorwfDEST

S5704A Tips & Tricks 17 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 17 Tips and Tricks Bit-ManipulationBit-Manipulation Bit Counter Count the number of "1" bits in a register. On exit, W contains the number of "1" bits in REG, and REG is scrambled. rrfREG,W andlw0x44 subwfREG movfREG,W andlw0x33 addwfREG rrfREG andlw0x11 addwfREG rrfREG swapfREG,W addwfREG,W andlw0x0F

S5704A Tips & Tricks 18 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 18 Tips and Tricks Bit-ManipulationBit-Manipulation Bit-Number [0-7] to Bitmask [ ] ; Enter with bit number [0-7] in BITNUM. Exits with bit mask in W. movlw0x01 btfscBITNUM,1 movlw0x04 movwftemp btfscBITNUM,0 addwftemp btfscBITNUM,2 swapftemp movftemp,w Bit-Number [0-7] to Bitmask [ ] ; Enter with bit number [0-7] in BITNUM. Exits with bit mask in W. movlw0x01 btfscBITNUM,1 movlw0x04 movwftemp btfscBITNUM,0 addwftemp btfscBITNUM,2 swapftemp movftemp,w

S5704A Tips & Tricks 19 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 19 Tips and Tricks Bit-ManipulationBit-Manipulation l Bit-Setting without Affecting W or Status Set to zero: clrfreg Set to a power of two: clrfreg bsfreg,bit Set to 255: clrfreg decfszreg Set a right-aligned group of bits: clrfreg;Set bits bsfreg,6;0-5. decfszreg; Set a left-aligned group of bits: clrfreg;Set bits decfszreg;4-7. bcfreg,4; incfszreg; General method, 2-4 bits set: clrf reg bsf reg,bit1 bsf reg,bit2 bsf reg,bit3 bsf reg,bit4 General method, 5-7 bits set: clrf reg decfsz reg bcf reg,unbit1 bcf reg,unbit2 bcf reg,unbit3

S5704A Tips & Tricks 110 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 110 Tips and Tricks DelaysDelays l Constant Delay Cycles WAIT MACRO CYCLES LOCAL X IF ((CYCLES) > 1027) ERROR "MUST BE <1028 CYCLES!" ENDIF IF ((CYCLES) < 0) ERROR "MUST BE >= 0 CYCLES!" ENDIF X = (CYCLES)%4 IF (X == 1) NOP ENDIF IF (X == 2) GOTO $+1 ENDIF IF (X == 3) NOP GOTO $+1 ENDIF X = (CYCLES)/4 IF (X) IF (X == 256) X = 0 ENDIF MOVLW X ADDLW -1 SKPZ GOTO $-2 ENDIF ENDM

S5704A Tips & Tricks 111 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 111 Tips and Tricks DelaysDelays l Non-Constant Delay Cycles SKIP: RRF COUNTER MOVLW 4 SUBWF COUNTER BCF COUNTER,6 BCF COUNTER,7 LOOP: NOP DECFSZ COUNTER GOTO LOOP RETURN MOVLW [NUMBER OF CYCLES] CALL DELAY.... ; DELAY CYCLES. ENTER WITH ; NUMBER OF CYCLES TO DELAY IN W. ; ; DELAY IS INCLUSIVE OF "MOVLW", ; “CALL”, AND “RETURN” OVERHEAD. DELAY: MOVWF COUNTER BTFSC COUNTER, 0 GOTO $+1 BTFSS COUNTER, 1 GOTO SKIP NOP GOTO $+1

S5704A Tips & Tricks 112 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 112 Tips and Tricks DelaysDelays Trading Stack Space for RAM Delay131072: call Delay16384 Delay114688: call Delay16384 Delay98304: call Delay16384 Delay81920: call Delay16384 Delay65536: call Delay16384 Delay49152: call Delay16384 Delay32768: call Delay16384 Delay16384: call Delay2048 Delay14336: call Delay2048 Delay12288: call Delay2048 Delay10240: call Delay2048 Delay8192: call Delay2048 Delay6144: call Delay2048 Delay4096: call Delay2048 Delay2048: call Delay256 Delay1792: call Delay256 Delay1536: call Delay256 Delay1280: call Delay256 Delay1024: call Delay256 Delay768: call Delay256 Delay512: call Delay256 Delay256: call Delay32 Delay224: call Delay32 Delay192: call Delay32 Delay160: call Delay32 Delay128: call Delay32 Delay96: call Delay32 Delay64: call Delay32 Delay48: call Delay32 Delay32: call Delay4 Delay28: call Delay4 Delay24: call Delay4 Delay20: call Delay4 Delay16: call Delay4 Delay12: call Delay4 Delay8: call Delay4 Delay4: return

S5704A Tips & Tricks 113 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 113 Tips and Tricks MathMath l 16-Bit Subtract with Valid Carry-Out movfSOURCE_LO,W;DEST = DEST - SOURCE. subwfDEST_LO;Note that the Z flag is movfSOURCE_HI,W;invalid after the skpc;subtraction. incfszSOURCE_HI,W; subwfDEST_HI ; l 8-Bit Add with Valid Carry-In/Out movfSOURCE,W;DEST = DEST + SOURCE + CARRY skpnc;Carry is valid after the incfSOURCE,W;addition. addwfDEST;

S5704A Tips & Tricks 114 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 114 Tips and Tricks MathMath l RAM-Efficient Moving-Window Average ;CALCULATE NEW_AVERAGE = (255 * OLD_AVERAGE + NEW_SAMPLE)/256. ;ENTER WITH THE NEW SAMPLE IN W. EXITS WITH THE NEW AVERAGE IN W. AVERAGE: addwfSUMLO;SUM = SUM + SAMPLE. movfSUMHI,W;(AND WHILE WE'RE HERE, PUT THE OLD skpnc;AVERAGE IN W). incfSUMHI; subwfSUMLO;ADJUST THE SUM BY SUBTRACTING THE OLD skpc;AVERAGE FROM THE NEW SUM. decfSUMHI; movfSUMHI,W;W=THE NEW AVERAGE (ADJUSTED SUM/256) return;RETURN.

S5704A Tips & Tricks 115 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 115 Tips and Tricks MathMath l Tricks with Known-Zero Registers  rlfKZ,W;DEST = DEST + SOURCE + CARRY. addwfSOURCE,W;Carry-out is only valid if SOURCE<255. addwfDEST;  rlfKZ,W;DEST = DEST CARRY. Carry-out is addwfDEST;valid.  movlw255;DEST = DEST CARRY. Carry-out skpc;is valid. addwfDEST;  rlfKZ,W;DEST = DEST + constant + CARRY, where addlw[constant];0 < constant < 255. Carry-out is addwfDEST;valid.

S5704A Tips & Tricks 116 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 116 Tips and Tricks MathMath l Even Parity ; Enter with input in register "X". Exits with ; even parity in bits 1, 2, 3, 4, and 5 of ;register "X". ; ; 7 words, 7 cycles. swapfX,W xorwfX rrfX,W xorwfX rrfX,W rlfX xorwfX

S5704A Tips & Tricks 117 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 117 Tips and Tricks MathMath l Even Parity ;Enter with input in register X. Branches to "ZERO" or "ONE" ;depending on parity. Doesn’t modify register X. For odd ;parity, replace "GOTO ZERO" with "GOTO ONE", and vice-versa. ;19 words. 5 or 7 cycles, including branch to ZERO or ONE. SWAPF X,W XORWF X,W ANDLW B ADDWF PC GOTO ZERO GOTO ONE GOTO ZERO GOTO ONE GOTO ZERO GOTO ONE GOTO ZERO GOTO ONE GOTO ZERO GOTO ONE ZERO:.... ONE:....

S5704A Tips & Tricks 118 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 118 Tips and Tricks MPASM Tips EQU vs. #define equ1equ5+3;MPASM will replace future ;occurrences of "equ1" with the ;value 8. #define def15+3;MPASM will replace future ;occurrences of "def1" with the ;string"5+3". xequ3*equ1;This line is equivalent to "x ;equ 3*8", so x = 24. yequ3*def1;THIS line, on the other hand, ;is equivalent to "y equ 3*5+3", ;so y = 18.

S5704A Tips & Tricks 119 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 119 Tips and Tricks MPASM Tips Accessing Registers Above 0x7F Method #1: REGEQUxxx - 128;Generates no warnings, but also....;doesn’t allow REG to be viewed MOVWFREG;in MPLAB Watch Windows. Method #2: MOVWFREG;Generates an MPASM warning. Method #3: MOVWFREG & 0x7F;Generates no warning, even when ;accidentally used with a ;page-0 register. Method #4: MOVWFREG ^ 0x80;Generates no warning when used ;correctly, but does generate a ;warning if accidentally used ;with a page-0 register.

S5704A Tips & Tricks 120 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 120 Tips and Tricks MPASM Tips l HIGH-and-LOW vs. Shift-and-AND BIGNUMEQU0x LSBEQULOW(BIGNUM);’LSB’ will always be set to ;0x56. MSBEQUHIGH (BIGNUM);Some versions of MPASM will ;set "MSB" to 0x12; others ;will set it to 0x34. SAFEMSBEQU(BIGNUM>>16) & 0xFF ;This method will always set ;"SAFEMSB" to 0x12.

S5704A Tips & Tricks 121 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 121 Tips and Tricks TimingTiming l Exact Sync to the TMR0 Prescaler ; Here, TMR0:PRE must be 01:3 or 02:0 BTFSS TMR0,BIT1 GOTO $+1 ; Here, TMR0:PRE must be 02:2 GOTO $+1 ; TMR0 always increments from 02 to ;03 right here. When we reload TMR0, ;we need to add 4 to the reload value ;because the MOVLW/MOVWF takes 2 ;cycles and there’s an additional 2- ;cycle synchronization delay. TMR0 ;will resume incrementing at EXACTLY ;the moment when it would have rolled ;over from 03 to 04. MOVLW RELOAD+4 MOVWF TMR0 ; Enter this section with TMR0 ; between 128 and 255, inclusive, ; and the prescaler divide-by- ; ratio set to divide-by-4. WAITFOR0: BTFSC TMR0,BIT7 GOTO WAITFOR0 ; Here, TMRO:PRESCALER can be ; 00:2 or 00:3 or 01:0. BTFSS TMR0,BIT0 GOTO $+1 ; Here, TMR0:PRE must be 01:1 ; or 01:2. GOTO $+1

S5704A Tips & Tricks 122 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 122 Tips and Tricks TimingTiming 16-Bit Pulse-Width Measurement with 5-Cycle Resolution ; Enter with PULSE_WIDTH_HI:LO set to Exits ; ; when PORT,PIN goes low. CHECK_PULSE: INCFSZ PULSE_WIDTH_LO DECF PULSE_WIDTH_HI BTFSC PORT,PIN GOTO CHECK_PULSE DONE: MOVF PULSE_WIDTH_LO,W ADDWF PULSE_WIDTH_HI

S5704A Tips & Tricks 123 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 123 Tips and Tricks Hardware Interfacing l Zero I/O-Pin PICmicro-to- PICmicro Communication Your Master PICmicro controls the Slave PICmicro's MCLR line. The Master normally keeps the Slave's MCLR line high (out of reset). When the Master wants to send a message, it pulls the Slave's MCLR line low, then pulls it high for a short time before pulling it low, then high again. The "message" is the time between MCLR-low pulses. Message error-proofing methods: Redundancy: Send the message two or more times and require that the Slave see consecutive, identical messages before acting on them. Parity: Send your message, then follow it with a "parity” message that brings the total time-between-MCLR-low-pulses time to some constant value. Framing: Send a unique-length "start of message" pulse, then your message pulse, then a unique-length "end of message” pulse. The Slave doesn't accept the message unless it sees the "start" and "end" pulses around it.

S5704A Tips & Tricks 124 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 124 Tips and Tricks l Setting ADCON0: Clock Select bits l 4 A/D clock (Tad) selections : l Fosc/2, Fosc/8, Fosc/32 and Frc(internal RC) l Tad Min. = 1.6 uS for V REF => 3.0V or 3.0uS for V REF < 3.0V For fastest A/D response, calculate the Tad which is closest to the Minimum value for Tad Example: V REF = 5.0V, Fosc = 4.0 MHz l For fastest A/D response, select Fosc/8 (2.0 uS). If Frc is selected, instead of Fosc/8, then Min. time would be 2.0us, but the Max. time would be 6.0us I.e. 3 times slower than the best A/D response time. l For fastest response, select Fosc = 5.0 MHz (Tad = 1.6uS) instead of 4.0Mhz (Tad = 2.0 uS). Hardware Interfacing

S5704A Tips & Tricks 125 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 125 Tips and Tricks l Setting ADCON0: GO/DONE l To start an A/D conversion the GO bit should be set to 1. Note: ADON and GO bit should not be set in the same instruction l On conversion complete, GO/DONE = 0 & ADIF = 1. Fastest check of A/D conversion completion: Bit test ADIF or the GO/DONE bit in “tight loop”. btfscADCON0,DONE goto$-1 Time for check = 3Tcycles l Checking A/D completion using Interrupts takes: 3T cycles for interrupt latency 10T cycles for Context Saving + 1T cycle for ADIF check Total = 14 T cycles Hardware Interfacing

S5704A Tips & Tricks 126 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 126 Tips and Tricks l A/D Conversion in Sleep l Reduces digital noise during A/D conversion. l Enable Frc mode for Tad l Enable or disable A/D Interrupt l Start A/D conversion and goto sleep l On A/D Completion: l If interrupt is enabled then CPU wakes up from sleep l If interrupt is disabled then CPU does not wake up from sleep, but A/D circuit is turned OFF (ADON is still set). l In Crystal mode conversion in sleep is slow since most crystals take 2 mS or more to wake-up l For fast conversion in sleep, use RC oscillator Hardware Interfacing

S5704A Tips & Tricks 127 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 127 Tips and Tricks MiscellaneousMiscellaneous l Direct Modification of PC (or PCL) For example, to calculate 2^W, where W is in the range [0-7]: TBL 1,2,4,8,16,32,64,128 assembles to: ADDWF PCL ADDLW 0 ADDLW -1 ADDLW -3 ADDLW -7 ADDLW -15 ADDLW -31 ADDLW -63 ADDLW 121 TBL:MACRO A,B,C,D,E,F,G,H LOCAL X ADDWF PCL X:ADDLW HIGH (A)+1 - HIGH (B) ADDLW HIGH (B)+1 - HIGH (C) ADDLW HIGH (C)+1 - HIGH (D) ADDLW HIGH (D)+1 - HIGH (E) ADDLW HIGH (E)+1 - HIGH (F) ADDLW HIGH (F)+1 - HIGH (G) ADDLW HIGH (G)+1 - HIGH (H) ADDLW HIGH (H)-7 IF ((HIGH $) != (HIGH X)) ERROR "TABLE CROSSES PAGE” ERROR “BOUNDARIES! DO” ERROR “SOMETHING!” ENDIF ENDM

S5704A Tips & Tricks 128 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 128 Tips and Tricks MiscellaneousMiscellaneous "Switch" Statement ; ENTER WITH VALUE TO BE TESTED IN W. XORLW VAL1 ;IF W = VAL1, GOTO CASE1. BZ CASE1 ; XORLW VAL2^VAL1 ;IF W = VAL2, GOTO CASE2. BZ CASE2 ; XORLW VAL3^VAL2 ;IF W = VAL3, GOTO CASE3. BZ CASE3 ; XORLW VAL4^VAL3 ;IF W = VAL4, GOTO CASE4. BZ CASE4 ; etc...

S5704A Tips & Tricks 129 © 1999 Microchip Technology Incorporated. All Rights Reserved. S5704A Tips & Tricks 129 Tips and Tricks ResourcesResources l PICLIST Internet Mailing List To subscribe, send to: with the following in the message body: subscribe piclist set piclist repro end l PICLIST Archives l l Embedded Control Handbook l PICLIST Internet Mailing List To subscribe, send to: with the following in the message body: subscribe piclist set piclist repro end l PICLIST Archives l l Embedded Control Handbook