READ WORD - read a word from the given address           (v40 sad)

 Command:       $AF $05
 Data:          $ww $xx $yy $zz

 read a word from address <$wwxxyyzz>  returns <$qqrr> as result

 Command will be ACK'ed when received.
 Command ACK:   $00 $05
 Command DONE:  $1F $05 $qq $rr

 BUGS
        This command does not return correct values in pre-V40 EXEC.