RANA Systems Elite Controller, User Manual

Page: 325 / 328

ELITE SERIES USER MANUAL APPEN. C - CP/M NOTES
possible. Replacing the simple math is a drive
mapping table which is dynamically filled-in
during the boot process with the physical slot
and drive numbers for each of the 16 possible
CP/M logical drives. (Note: The table has room
for 16 drive entries, but there are only enough
DPH’s allocated for 8 drives.)
The cold start initialization code scans all
cards in the Apple and determines which are Disk
IX controllers, which are Elite Controllers, and
which are non-disk I/O cards. The scanning goes
in reverse order from slot 7 back down to slot
1. Whenever a disk controller is found, the
next two or four CP/M logical drives (depending
on which controller was found) are mapped (in
the mapping table) to that controller card ‘s
drives.
The mapping table consists of two parts: the
slot numbers times 16 for each of the CP/M
drives (A:-P:), followed by the drive number of
the controller for the 16 CP/M drives. Both
parts consist of single byte elements. If the
SELDSK vector is called with [C] equal to 0
(drive A:), then [IX] will return pointing to
drive A:’s slot*16 entry which is also the base
address of the mapping table. Drive A: ‘s drive
number of that controller card can be found at
[IX]+ 16.
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