( With dst being assumed to be an AT28 EEPROM, perform !
  operation while doing the right thing. Checks data integrity
  and ABORT on mismatch. )
: AT28! ( n a -- )
    2DUP C!
    ( as long as writing operation is running, IO/6 will toggle
      at each read attempt. We know that write is finished when
      we read the same value twice. )
    BEGIN ( n1 a )
        DUP C@      ( n1 a n2 )
        OVER C@     ( n1 a n2 n3 )
    = UNTIL
    ( We're finished writing. do we have a mismatch? )
    C@ = NOT IF ABORT" mismatch" THEN
;
