Brads Electronic Projects Forum

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draw_ball				;	this routine draws the ball on the screen
	movf ball_y, w		;	copy our ball_y co-ordinate to w
	movwf PORTB			;	and then to portb (our data bus)
	bsf PORTA, 2		;	now latch this 8-bits to the green 74373
	bcf PORTA, 2		;	and now close the latches
	movf ball_x, w		;	copy ball_x co-ordinate to w
	movwf PORTB			;	then to port b (our data bus)
	bsf PORTA, 4		;	now latch this 8-bits to the COLUMN data 74373
	bcf PORTA, 4		;	and close the latches
	bcf PORTA, 3		;	enable both the green and column 74373 outputs
	bcf PORTA, 6		;	3 is green and 6 is column data
	call delay			;	hold this data on the screen for a split second
	bsf PORTA, 3		;	close both green and column outputs
	bsf PORTA, 6		;	3 is green and 6 is column data
	return				;	and return to the main program