;Name: .asm
; By Edgardo Gonzalez

; This Program takes input from port 1 from a quadrant shaft encoder
; to increment or decrement a variable for use elsewhere. Here the variable


; *****************************Equates*******************************
echo equ p3.0 ;Equates "echo" to address p3.0
init equ p3.1 ;Equates "init" to address p3.1

; ***************************Main Program****************************

org 00
mov TMOD, #01H ;Use both timers ... T0=16 Bit timer mode T1=13 Bit timer mode
lcall INTB ;Allows sensor to finish internal blanking

MAIN:
mov R0,#10 ;Sets how many times R0 is going to repeate
clr init
;mov P3,#0

LOOP: mov TH1,#00 ;Sets the timer
mov TL1,#00 ;;;;; to zero
setb TR1 ;Starts the Timer 1
setb init ;Sends out the pulse
WAIT2: jnb echo,wait2 ;Waits untill there is a return signal
clr TR1 ;Stops Timer 1
clr init ;Stops sending the pulse
clr TF1 ;Clears the overflow flag in Timer 1

mov R1,TH1
mov p1,r1

ret

; *******************************Sub Routines************************

INTB: mov TH0,#-04H ;Set the timer for approximitly
mov TL0,#-0F8H
setb TR0 ;Starts Timer 0
WAIT: jnb TF0,wait ;Waits till the overflow flag is set
clr TR0 ;Stops Timer 0
clr TR0 ;Clear overflow flag in Timer 0
ret






end