please dont rip this site

SX Specific Pulse Width Measurement

By Nikolai Golovchenko

; 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


file: /Techref/scenix/lib/io/osi1/sensor/plusewidth-ng.htm, 8KB, , updated: 2001/5/19 20:23, local time: 2024/12/14 11:11,
TOP NEW HELP FIND: 
18.97.14.91:LOG IN

 ©2024 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?
Please DO link to this page! Digg it! / MAKE!

<A HREF="http://www.sxlist.com/techref/scenix/lib/io/osi1/sensor/plusewidth-ng.htm"> SX Specific Pulse Width Measurement </A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.


Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?

 

Welcome to sxlist.com!


Site supported by
sales, advertizing,
& kind contributors
just like you!

Please don't rip/copy
(here's why

Copies of the site on CD
are available at minimal cost.
 

Welcome to www.sxlist.com!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  .