;
; ***************************************************************************
; ***  Bubble Software Parallax to PIC Source Converter. Copyright 1999.  ***
; ***  http://www.picnpoke.com                 email: sales@picnpoke.com  ***
; ***************************************************************************
;
; PULSIN port (in w), pin, state
; Measures the width of an input pulse in 10-cycle (10 us at 4 MHz) units.
; Returns a 16-bit (0 to 65,535) value. If no pulse occurs within
; 65,535 10-cycle intervals, the routine returns an error code in w.
; Routine is edge triggered. If the input pin is already in the target state
; when the routine begins, it will wait for the state to change, then wait
; for the specified edge. The routine waits 65,535 x 10 cycles for
; each edge, so it normally returns within 0.65535 seconds (4 MHz).
; However, if each transition is delayed by close to the full 65,535 x 10
; cycles, the routine can take nearly 2 seconds to return (4 MHz).

	P = pic16c55
	#include <16c55.inc>   ; processor assembler definitions
	_CONFIG _xt_osc & _wdt_off & _protect_off
 reset start
	
 org 8
pin Res d'1'  ; Pin number to sample (0-7).
state Res d'1'  ; Trigger: 255 = 0-to-1 transition.
hiB Res d'1'  ; MSB of measurement.
lowB Res d'1'  ; LSB of measurement.

; Device data and reset vector
 org 0
; Table to convert pin number (0-7) into bit mask (00000001b to 10000000b).

Pinz         ADDWF pcl                  
             RETLW d'1'                 
             RETLW d'2'
             RETLW d'4'
             RETLW d'8'
             RETLW d'16'
             RETLW d'32'
             RETLW d'64'
             RETLW d'128'

start        MOVLW d'0'                 ; Outputs to display result on LEDs.
             TRIS 6h
             MOVLW d'0'                 
             TRIS 7h
             MOVLW b'00001111'          ; All inputs
             TRIS 5h
             MOVLW d'0'                 ; Negative pulse.
             MOVWF state
             MOVLW d'2'                 ; Pin 2.
             MOVWF pin
             MOVLW d'0'                 ; Port ra.
             CALL Pulsin                
             MOVF lowB,w                ; Write Pulsin result to ports RB
             MOVWF 6h
             MOVF hiB,w                 ; and RC for viewing on LEDs.
             MOVWF 7h
             GOTO start                 ; Do it again.

; Upon entry, the desired pin must already be set up as an input.
; The w register contains a number representing the input port (0-2) for
; RA through RC. Variable pin contains the pin number (0-7). Variable state
; contains 255 for a 0-to-1 (positive) pulse, or 0 for a 1-to-0 (negative) pulse.

; Upon exit, the 16-bit count is in variables lowB and hiB.
; Variable pin contains the mask bit used by pulsin (not the pin number
; anymore, but a value with a 1 in the pin position), and state has been
; ANDed with pin. W contains the error code: 0= no error; 1= pin in
; already in target state when Pulsin was called--timeout waiting
; for transition; 2= timeout waiting for initial edge; 3= timeout waiting
; for final edge.

Pulsin       CLRF lowB                  ; Clear the 16-bit counter.
             CLRF hiB                   
             MOVWF fsr                  ; Point to the port number.
             MOVLW 5h                   ; Add offset for port RA.
             ADDWF fsr
             MOVF pin,w                 ; Get bit mask from the table.
             CALL Pinz                  
             MOVWF pin                  ; Put the mask into pin.
             ANDWF state                ; Mask extra bits out of state.
Pulsin_Hold  MOVF indirect,w            ; Sample the port.
             ANDWF pin,w                ; Mask off bits other than pin.
             XORWF state,w              ; Check pin against state.
             BTFSS status,z             ; If pin <> state, set up for edge.
             GOTO Pulsin_doneH
             INCF lowB                  ; Otherwise, lowB = lowB+1.
             BTFSC status,z             ; Overflow in lowB?
             INCFSZ hiB                 ; Yes: hiB=hiB+1, watch for overflow.
             GOTO Pulsin_Hold           ; Sample the pin again.
             RETLW d'1'                 ; Overflow in hiB? Timed out: return.
Pulsin_doneH CLRF lowB                  
             CLRF hiB                   
Pulsin_Edge1 MOVF indirect,w            ; Sample the port.
             ANDWF pin,w                ; Mask off bits other than pin.
             XORWF state,w              ; Check pin against state.
             BTFSC status,z             ; If pin = state, wait until change.
             GOTO Pulsin_doneE
             INCF lowB                  ; Otherwise, lowB = lowB+1.
             BTFSC status,z             ; Overflow in lowB?
             INCFSZ hiB                 ; Yes: hiB=hiB+1, watch for overflow.
             GOTO Pulsin_Edge1          ; Sample the pin again.
             RETLW d'2'                 ; Overflow in hiB? Timed out: return.
Pulsin_doneE CLRF lowB                  
             CLRF hiB                   
Pulsin_Edge2 MOVF indirect,w            ; Sample the port.
             ANDWF pin,w                ; Mask off bits other than pin.
             XORWF state,w              ; Check pin against state.
             BTFSS status,z             ; If pin <> state, we're done.
             GOTO Pulsin_done
             INCF lowB                  ; Otherwise, lowB = lowB+1.
             BTFSC status,z             ; Overflow in lowB?
             INCFSZ hiB                 ; Yes: hiB=hiB+1, watch for overflow.
             GOTO Pulsin_Edge2          ; Sample the pin again.
             RETLW d'3'                 ; Overflow in hiB? Timed out: return.
Pulsin_done  RETLW 0h                   ; Done: pulsewidth in hiB, lowB.
             
             
             end