WRITE WORD - write the given data to the address given

 Command:       $AF $02
 Data:          $ww $xx $yy $zz $qq $rr

 write the word <$qqrr> to address <$wwxxyyzz>

 Command will be ACK'ed when received.
 Command ACK:   $00 $02
 Command DONE:  $1F $02