>>>> "Gooijen" == Gooijen H
<Gooijen> writes: 
 Gooijen> Well, let's try to give an answer.  The SWitch Register is
 Gooijen> what is says: *switch* register.  So you can read the
 Gooijen> switches from it, but writing to it is no use.  Don't shoot
 Gooijen> me if I am mistaken!  From memory, the address is 777570.
The switches are read-only at 777570; the display register is
write-only at the same address.
           paul