To: Atari Bob
Subject: RE: Small Questions re: the 1200xl Hotkeys..




The partition table at $D7C0 has 16 entries of 4 bytes each. Each entry is
the data for a drive partition, of which there can be an almost infinite
number. The entry specifies on what actual drive sector times 256 the
partition starts and how many 256 sector blocks the partition has allocated
on the drive. It also sets the drive type: SD, ED or DD and which SIO
address it will be selected as: D1 thru D9.

Pressing CNTL F1 cycles the first seven entries in this table as D1. Every
time you press CNTL F1 the next drive in the sequence becomes what you see
in D1. When you reach address $D7DC, you jump back to $D7BC which is not
actually in the table. This deselects the HD altogether and you use the SIO
device. Look at locations $D7B0 thru $D7FF with BUG from the EDASM cartridge
( enter:   DD7B0,D7FF  ). Watch the change in the last byte of each four
byte block as you press CNTL-F1 (you have to display after each time). You
will see the 1 in the last half of the byte move down one entry for each
keypress.


OK?

Bob