I copied some code out of Easy PIC'n and can't get it to work.  Does anyone know why?  It is supposed to look at the inputs of porta and send the output to portb.  When I power it up, portb shows the status of the inputs, but if the inputs are changed while the chip is still powered up, the outputs don't change.  Also if MCLR is set low and then high the outputs still don't change.  The only way to get the outputs to change is to power down the chip and power it back up. Here is the code:

 

;=======PICT1.ASM=====================5/27/98
 INCLUDE <P16F84.INC>
 
;--------------------------------------------
; Configuration bits
 __CONFIG _RC_OSC & _PWRTE_ON & _WDT_OFF & _CP_OFF
;--------------------------------------------
; cpu equates (memory map)
porta equ 0x05
portb equ 0x06
;--------------------------------------------
 org 0x000
;
start movlw 0x3f ;load W with 0xff
 tris porta ;set porta to contents of W
;
 movlw 0x00 ;load W with 0x00
 tris portb ;set portb to contents of W
;
 movf porta,w ;read porta, load into W
 movwf portb ;load file register, portb with W
;
 NOP
 NOP
 goto start ;goto begining
;
 end
;-------------------------------------------------
;at blast time, select:
; memory unprotected
; watchdog timer disabled (default is enabled)
; standard crystal (using 4 MHz osc for test)
; power-up timer on
;=================================================