Neat 2SIO trick
 

I have a 2SIO addressed to ports 0/1 for CP/M and 20/21 for MITS stuff. So I lifted pin 3 of the L30 (IC O) and tied it to pin 12 of the same IC.

Now my 2SIO will respond to either I/O locations. : )

Here is the modification for the address trick. Wire A4 does not matter any more after this mod.

Lift pin 3 and solder a jumper from it to pin 12, but leave pin 12 in the socket.

If you are careful solder won't go into the socket. Or you can pull the chip out first. :)

http://www.stockly.com/images3/07112...-21-1_3547.jpg

http://www.stockly.com/images3/07112...-21-2_3548.jpg

http://www.stockly.com/images3/07112...-21-3_3549.jpg