BASIC CART MODIFICATION
Installing a switch on the cart so Basic can be
switched on or off without removing the cart

I own an Atari 800 and about half the time use the Basic cartridge. 
Other times I use programs that require that the Basic cartridge be
removed.  This can cause a lot of wear and tear on the 800's 
cartridge slot.  To avoid this, the cart can be modified so it can be 
switched in or out.  I took apart my Basic cart, removing the shell. 
I cut the circuit board trace connecting pins 13 and 14 on the 
cartridge board (pin 14 is the source of memory map control signal
RD5).  I installed a very small (approx. half inch long, and 
quarter inch tall from the bottom of the switch body to top of 
slider) slide switch (SPDT) on the top edge of the board, center 
contact soldered to the +5V trace (the fat trace at the top IC side 
of the board).  The other contact is connected to pin 14.  This 
connection is made as far from the bottom edge of the board as 
possible so it can be pluged into the 800's cart slot without 
jamming.  The metal housing of the switch should be connected to the 
+5V trace to form a static drain (be sure it doesn't short to the 
access door's metal shield; the metal shield could be removed if 
necessary).  The cart board is inserted with the chips facing to 
the back of the 800.
When I want to use Basic, I open 
the access door and set the switch to "B".  When I need to remove 
Basic, I turn the switch to "M", for machine code programs.  This 
causes the circuits in the Atari 800 to switch away from the cart 
and to the RAM at the same addresses.  The cart is effectively
removed.  I rarely use other carts, but if I want to, I can still 
unplug the modified Basic cart.


       switch 
_________________
I     +5 trace  I
I  ----   ----  I
I  IicI   IicI  I
I  I  I   I  I  I
I  I__I   I__I  I
I               I
I               I
  edge card conn.
  +5V-pin 13^ ^pin 14-RD5

     plug board into computer so that the ic's face
      the back of the computer