;
; ***************************************************************************
; ***  Bubble Software Parallax to PIC Source Converter. Copyright 1999.  ***
; ***  http://www.picnpoke.com                 email: sales@picnpoke.com  ***
; ***************************************************************************
;
; LOW port (in w), pin
; Outputs a low to the specified port and pin.

; Device data and reset vector
	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 set (0-7).

; Variables for the demo program--not required by Low.
p_index Res      d'1'       ; Copy of pin number, port number.
temp    Res      d'1'       ; Temporary variables for time delay
temp2   Res      d'1'       ; between outputs.

        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'

; The following demonstration code should show the value of being able to
; clear a particular bit of a port based on a calculation performed while the
; program is running. As the variable p_index is incremented from 0 to 15,
; it is used to specify the pin and port to clear using Low.

start        MOVLW d'0'                 ; All outputs on rb.
             TRIS 6h
             MOVLW d'0'                 ; All outputs on rc.
             TRIS 7h
             MOVLW d'255'               ; Start with 1s on rb, rc (all LEDs on).
             MOVWF 6h
             MOVLW d'255'               
             MOVWF 7h
             CLRF p_index               ; Clear p_index.
start_loop   MOVLW d'7'                 ; Copy three lsbs of p_index into
             MOVWF pin
             MOVF p_index               ; variable pin.
             ANDWF pin
             MOVLW d'1'                 ; IF p_index.3 = 0
             BTFSC p_index,d'3'         ; THEN w = 1
             MOVLW d'2'                 ; ELSE w = 2
             CALL Low                   
             CALL delay                 ; Wait a while between lows. 
             INCF p_index               ; Next pin/port.
             BTFSS p_index,d'4'         ; IF p_index < 15 (rc.7)
             GOTO start_loop            ; THEN :loop ELSE done
done         GOTO $                     ; Endless loop.


; To use the routine Low, put the pin number into the variable pin
; and the port number into w. Then call Low. 

Low          MOVWF fsr                  ; Point to the port number.
             MOVLW 5h                   ; Add offset for port RA.
             ADDWF fsr
             MOVF pin,w                 
             CALL Pinz                  ; Get bit mask from the table.
             XORLW 0xFF                 ; Invert it so there's a 0 in selected bit.
             ANDWF indirect             ; Turn off the selected bit
             RETLW 0h                   

; Delay routine for demonstration. Not required by Low.

delay        DECFSZ temp                ; Time delay to provide spacing
             GOTO delay
             DECFSZ temp2               ; between highs.
             GOTO delay
             RETLW 0h                   

             
             
             end