The Timer1 interrupt is just to exit the SERIN2 line and clear the decoder output pins if
no data has been received before Timer1 times-out.

Without the interrupt, it would just sit & spin on the SERIN2 line due to noise on the RF
receivers data output pin.

If data IS received, it drops to the next line after the SERIN2 and disables the timer until
it's needed again.

If you need to put certain values on PORTB or PORTA just use something like;

movlw b'11000010' ; <-- value to place on port
movwf PORTB ; <-- put it on the port

Not much tougher than PORTB = %11000010 in PBP...;o)