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INPUT/OUTPUT PROVISIONS
26.2 -- Device Independent liD
26.2. 1. 1 CDBlOC --
CUT",..ent
IOCB
address
These
two-bytes
of
the
CDB
are reseT"ved
for
expansion.
They are currently not being
used
by
the
device
d,..ivers.
These two bytes should
be
initialized to zero.
26.2.1.2 CDBSDA -- Sortware driver address
This
two~byte
rield or the CDS must contain the starting
address of
the
device
driver
program
that
contT"ols
the
device.
It
is
this
addT"ess
that
is
used to access the
individual device dT"ive-r entry points.
Therefore,
this entl'Y
must
be
pT"ovided
in
every
CDB.
The fOT"mat
of
the device
drive~
i~
explained in section 26.2.2.
26.2.1.3 CDBHAD -- Hardware address
These two bytes
of
the
CDB are
intended to
contain
the
lowest
address
of the haT"dware device
(PIA
or
ACIA)
used to
interface with the external device.
The actual usage of this
coa
entTY
depends exclusively on the device driver progT"am.
The device independent
liD
functions
do
not
access
this
entT""l.
26.2.1.4
CDBDDF -- Device descT'.iptor flags
The CDBDDF byte contains the basic description about the
types of liD accesses
that
the
device
can
perform.
The
fOT"mat or the CDBDDF byte is shown below:
7
6
5
4
3
2
1
o
l R :
a :
I : F : W : S : L : D :
Default binary format
Logical sector
liD
flag
System console flag
Rewindable device
r~ag
File-type device flag
Input device flag
Output device flag
ReseT"vable device flag
These
flags
aT"e
constant once defined.
The flags are
interrogated
by
the various device independent
IIO
functions
in
order
to
verify. that
the
T'~Q.uested
function
can be
performed on the specified device.
The
properties controlled
by the various bits of the
COBODF
are explained below.
.J
Page
26-04
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