Specifications

Apple II Technical Notes
Apple IIGS
4 of 7 #69: The Ins and Outs of Slot Arbitration
Bit Encoded Slot Configuration
F E D C B A 9 8 7 6 5 4 3 2 1 0
0
1 = slot 1 active
1 = slot 2 active
1 = slot 3 active
1 = slot 4 active
1 = slot 5 active
1 = slot 6 active
1 = slot 7 active
0
1 = slot 9 active
1 = slot 10 active
1 = slot 11 active
1 = slot 12 active
1 = slot 13 active
1 = slot 14 active
1 = slot 15 active
Figure 2–Bit Encoded Slot Configuration
By fully using the slot number parameter, the Slot Arbiter returns any aspect of the current slot
configuration. Following are a few examples:
Slot number Action Taken by Slot Arbiter
$8000 Returns current Bit Encoded Slot Configuration in
the X register. This number asks the Slot Arbiter to
switch in with no slot dependencies (no switching),
so it just returns the Bit Encoded Slot
Configuration.
$0300 Restore from Bit Encoded Slot Configuration. This
command, when paired with the one above, can be
used to save and restore a slot environment.
$0005 Asks the Slot Arbiter for internal port 5.
The Impact on Applications and Drivers
Applications which correctly do all input and output through GS/OS are affected by slot
arbitration, except that they find more devices available. GS/OS uses the slot number parameter
in the Device Information Block to call the Slot Arbiter, making sure the slot is available for the