North Star MDS-A-O User Manual page 30

DISK CONTROLLER COMMANDS
Commands to the disk controller are specified
by
memory read
~-/' references to addresses within a particular lK byte block of the
CPU address space. The lK byte block subdivides into four cases.
In all cases the high order 6 address bits (BS) are used to
determine if the lK block is addressed (i.e. the controller board
is selected). The next two bits determine the subcase and the
use of the low order eight bits depends on the subcase.
CASE 0 PROM addressing
Read byte from the
256
bytes of PROM.
CASE
1
write byte of data
as
1
Data
write a byte of data to
register is not empty.
byte to be written.
the
The
disk. Wait
low order 8
if the write
bits specify
shift
the
CASE 2
Controller Orders
as
2 1001
ss
IDPI STI
OS
Load a-bit order register from low order 8 address bits.
DD Controls density on write 00-1 for double density and
DOsS for single density.
•
SS Specifies the side
of a
double-sided diske~~. The
bottom side (and only side of a single-sided diskette)
is selected when SS=8. The second (top) side is
selected when SS-l.
. North Star MICRO-DISK System
30