SX Specific Pulse Width Measurement

; Pulse width capture test ; ; Board: SX Demo/Proto Board ; ; Three routines are tested - 8 bit, 16 bit, and 24 bit. The resolution ; is 4 cycles in every case. Testing is done manually in step mode. ; ; A routine is selected by three buttons at RB3, RB2, RB1: ; ; RB3=0 - 8-bit ; RB2=0 - 16-bit ; RB1=0 - 24-bit ; ; A pulse is generated manually by pressing a button at RB0. ; ; The pulse measurement code is based on Scott Dattalo's idea. ; ; May 10, 2001 ; by Nikolai Golovchenko DEVICE SX28L, OSCHS2, TURBO, STACKX, OPTIONX RESET start ORG $08 ;global bank pulse0 DS 1 ;LSB of the counter pulse1 DS 1 pulse2 DS 1 ;MSB ORG $10 ;bank0 ORG $30 ;bank1 ORG $50 ;bank2 ORG $70 ;bank3 ORG $90 ;bank4 ORG $B0 ;bank5 ORG $E0 ;bank6 ORG $F0 ;bank7 RA_DIR EQU %00000000 RB_DIR EQU %00001111 ;RB.0 .. RB.3 - button inputs RC_DIR EQU %00000000 ;input port pins but_8 EQU RB.3 but_16 EQU RB.2 but_24 EQU RB.1 pulse EQU RB.0 OPTION_INIT EQU $7F ;OPTION load value ;x--- ---- 0 = register 01h addresses w ;-x-- ---- 1 = RTCC roll-over interrupt is disabled ;--x- ---- 1 = RTCC increments upon transition on RTCC pin ;---x ---- 1 = RTCC increments on high-to-low transitions ;---- x--- 1 = Prescaler is assigned to WDT, and divide rate on ; RTCC is 1:1 ;---- -xxx 111 = Prescaler divider 1:128 (WDT) ;**************************************************************************** ; Start of program ;**************************************************************************** ORG $000 ;page 0 start ;init ports clr RA clr RB clr RC mov w, #RA_DIR mov !RA, w mov w, #RB_DIR mov !RB, w mov w, #RC_DIR mov !RC, w ;load option and make w addressable mov w, #OPTION_INIT mov !OPTION, w ;**************************************************************************** ; Main loop: ; 1) wait a transition in pulse from 0 to 1 ; 1) select the test routine ; 2) measure the pulse width ; 3) goto 1 ;**************************************************************************** loop ;wait the low to high transition snb pulse jmp $-1 sb pulse jmp $-1 ;select and run the test routine call select ;repeat jmp loop ;selection routine select sb but_8 jmp mpulse8 ;call pulse8 and return sb but_16 jmp mpulse16 ;call pulse16 and return sb but_24 jmp mpulse24 ;call pulse24 and return retp ;if nothing selected just return ;**************************************************************************** ; 8 bit pulse width measurement at 4 cycle resolution ; ; Return values at check points A and B (see below) will be: ; Check point: A B A B A B A B ... ; Counter value: 1 2 3 4 5 6 7 8 ... ; ; Size: 11 instruction words ;**************************************************************************** mpulse8 mov w, #1 ;init counter mov pulse0, w mov w, #2 ;init increment size mpulse8_loop sb pulse ;check input the first time (A) jmp mpulse8a ; if low, exit add pulse0, w ;increment counter by two nop ;wait a cycle to sample at an equal interval ;instead of nop we can restart the watchdog: ; clrwdt ;or check the counter overflow: ; sc snb pulse ;check input the second time (B) jmp mpulse8_loop ;here the pulse end was detected after the second input check - correct the ;counter clrb pulse0.0 mpulse8a ;here the pulse end was detected after the first input check - leave the counter ;unchanged; if we fall here from the second input check, don't change counter ;either. retp ;return ;**************************************************************************** ; 16 bit pulse width measurement at 4 cycle resolution ; ; Return values at check points A, B, and C (see below) will be: ; Check point: A B C A B C A B C A ... ; Counter value: 0 1 2 3 4 5 6 7 8 9 ... ; ; Size: 23 instruction words ;**************************************************************************** mpulse16 clr pulse0 ;clear LSB of the counter clr pulse1 ;clear MSB of the counter mov w, #3 ;init increment size mpulse16loop sb pulse ;check input the first time (A) jmp mpulse16a ; if low, exit add pulse0, w ;increment counter by three nop ;wait a cycle to sample at an equal interval ;instead of nop we can restart the watchdog: ; clrwdt ;or check the counter overflow: ; sb pulse1.7 - counter value is limited to 0..32770 ;or: sb pulse1.6 - counter value is limited to 0..16387 ;or: sb pulse1.5 - counter value is limited to 0..8197 ;or: sb pulse1.4 - counter value is limited to 0..4099 ; sb pulse ;check input the second time (B) jmp mpulse16b snc ;propagate carry to the higher byte inc pulse1 ; snb pulse ;check input the third time (C) jmp mpulse16loop ;here we construct the correction value in w according to the check point - ;A (w = 0), B (w = 2), or C (w = 1). Then counter is then corrected - ;pulse = pulse - w. ;point C entry xor w, #$03 ;3^3^2^3 = 1 clc ;clear carry to avoid following carry propagation ;point B entry mpulse16b xor w, #$02 ;3^2^3 = 2 snc ;propagate carry if we didn't finish the addition inc pulse1 ; ;point A entry mpulse16a xor w, #$03 ;3^3 = 0 ;correct counter sub pulse0, w sc dec pulse1 ;return retp ;**************************************************************************** ; 24 bit pulse width measurement at 4 cycle resolution ; ; Return values at check points A, B, C and D (see below) will be: ; Check point: A B C D A B C D A B C D A ... ; Counter value: 3 4 5 6 7 8 9 10 11 12 13 14 15 ... ; ; Size: 39 instruction words ;**************************************************************************** mpulse24 clr pulse0 ;clear LSB of the counter clr pulse1 ;clear middle byte of the counter clr pulse2 ;clear MSB of the counter mov w, #1 ;init increment size mpulse24loop sb pulse ;check input the first time (A) jmp mpulse24a ; if low, exit add pulse0, w ;increment counter by one nop ;wait a cycle to sample at an equal interval ;instead of nop we can restart the watchdog: ; clrwdt ;or check the counter overflow: ; sb pulse2.6 - counter value is limited to 0..2^24 ;or: sb pulse2.5 - counter value is limited to 0..2^23 ;or: sb pulse2.4 - counter value is limited to 0..2^22 ;etc... ; sb pulse ;check input the second time (B) jmp mpulse24b snc ;propagate carry to the higher byte add pulse1, w ; sb pulse ;check input the third time (C) jmp mpulse24c snc ;propagate carry to the higher byte add pulse2, w ; snb pulse ;check input the fourth time (D) jmp mpulse24loop ;here we construct the correction value in w according to the check point - ;A (w = 3), B (w = 0), C (w = 1), or D (w = 2). Then counter is then corrected - ;pulse = (pulse << 2) + w. ; ;for simplicity, the two lower bits can be shifted into pulse, but the bits ;should be reversed: ;A (w = 3), B (w = 0), C (w = 2), or D (w = 1) ;point D entry xor w, #$03 ;1^3^2^3^2 = 1 clc ;clear carry to avoid following carry propagation ;point C entry mpulse24c xor w, #$02 ;1^2^3^2 = 2 snc ;propagate carry if we didn't finish the addition inc pulse2 ; clc ;clear carry to avoid following carry propagation ;point B entry mpulse24b xor w, #$03 ;1^3^2 = 0 snc ;propagate carry if we didn't finish the addition incsz pulse1 ; dec pulse2 ; inc pulse2 ; ;point A entry mpulse24a xor w, #$02 ;1^2 = 3 ;correct counter rr WREG rl pulse0 rl pulse1 rl pulse2 rr WREG rl pulse0 rl pulse1 rl pulse2 ;return retp ;**************************************************************************** ORG $200 ;page 1 ORG $400 ;page 2 ORG $600 ;page 3

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