The code below will load FF to PORTA, however not all pins on the 628A can be used as outputs.
First you must set up the Configuration line to Set the Internal Oscillator On so allowing RA6 and RA7 to be used as Digital pins instead of an input for the crystal oscillator.
You then must turn off the default Comparator function, to allow all PortA pins to be used as Digital outputs
Finally RA5 can only be used as a Digital Input, and only when Mclre is turned off in the Config.
So the final result on PortA for the 255 input will be 0xDF or 223. No value in bit RA5
You are just using the code in the most basic way possible, have a look at the TEMPLATE file for the 628A in MPlab /Asm directories, which give you all the basics.
Code:
LIST p=16F628a
include "P16F628a.inc"
__CONFIG _LVP_OFF & _BOREN_OFF & _MCLRE_OFF & _WDT_OFF & _PWRTE_ON & _INTOSC_OSC_NOCLKOUT
banksel TRISA ; select bank1
movlw b'00000000'
movwf TRISB
movwf TRISA
banksel PORTA ; return to bank 0
movlw 0x07 ; TURN OFF PORTa COMPARATOR
movwf CMCON
movlw d'255'
movwf PORTA
movwf PORTB
NOP
NOP
end