Here goes my code for 16F676. Used this IC because I can program it in PICKIT2 & also I have jumpered my sensor around it.
Code:
Include "modedefs.bas"
DEFINE     NO_CLRWDT    1
DEFINE          OSC     4       ' OSCCON defaults to 4MHz on reset
DEFINE OSCCAL_1K 1

@ __Config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _BODEN & _CP & _CPD

PAUSE 50
Tx Var PortA.1
Rx Var PortA.0
power var PortC.1
	TRISA = %000001
	TRISC = %000001
	CMCON = 7
	ANSEL = 0
      OPTION_REG = %10000111  ' RAPU = off, PS 1:256 to TMR0
	PORTA=0
	PORTC=0
	' setup iZCD to interrupt on change
	INTCON = 0

; PortC.0 = PWM Receive ; ; ; ; ; PortC.1 = Power_On ; ; ; ;  PortA.0 = Receive Pin ; ; ; ; PortA.1 = Transmit Pin ; ; ; ; PortA.2=Trigger Pin

main:
High power
pause 100
Serout Tx, N9600, ["0x44+0x00+160+ ???"]	;	To set lower threshold distance to appx 3 meters. What should be the SUM & how do you calculate it?
Serout Tx, N9600, ["0x44+0x01+250+ ???"]	;	To set upper threshold distance to appx 5 meters
Serout Tx, N9600, ["0x44+0x02+0xaa+ ???"] ; 	To set operation mode to autonomous mode

	if PortA.2=0 then
		High PortC.2 ; led 1
	else
		high PortC.5 ; led 2
	endif
goto main
end
1) How do you calculate the SUM? any example please
Once I get to the next point, I will update here if I get stuck. Thanks