A-2 HP 9895A Disc Memory Command
Set
Command
Compatibility
The 9895A belongs
to
a set of
command
compatible HP-IB interface discs.
All
of these discs
meet
the
"HP-300
Compatible HP-IB" standards.
In
addition, the same
sequence
of HP-IB
operations can
be
used
to
transfer data to
and
from any of these discs.
There are
some
subtle differences between
HP-300
Compatible HP-IB
and
IEEE
Standard
#488-1978.
1.
An
identify code
sequence
by the host to determine what class of devices
and
which
device
is
connected, is not supported by IEEE
#488-1978.
2. Disc read
and
write operations cannot
be
suspended
and then resumed; i.e.,
an
Untalk
or
Unlisten command terminates
command
operation. This
is
not consistent
with IEEE
#488-1978.
Sipce the capacity
and
organization of a flexible disc is different from
other
HP-IB compati-
ble discs, the allowable range of certain parameters
is
also different from the
other
discs.
Certain commands used in formatting a disc
or
for diagnostic purposes
are
unique to the
9895A. Similarly, certain commands supported by other discs are not
supported
by the
9895A.
An
unrecognized command causes
an
error to
be
set, but has
no
detrimental effect
on
controller operation.
Command
Sequences
Much of the 9895A command
set
shown in this section
is
made
up from two basic types of
HP
-IB
sequences.
To send information (commands
or
data)
to
the 9895A, the bus controller addresses
it
to
listen,
and
then
sends
a secondary command byte followed by a series of information bytes.
,.,
The last information byte sent must be tagged with
an
EOI. Finally,
the
bus controller sends
an
Unlisten command,
and
the
sequence
is complete.
To
receive information (status
or
data) from the 9895A, the bus controller addresses it
to
talk,
and
then
sends
a secondary
command
byte.
At
this point
the
device
sends
back
a series
of information bytes. In
some
cases the last information byte
will
be
tagged with
an
EOl. In
cases where the last information byte
is
not
tagged with
an
EOI,
an
additional byte tagged
with
an
EOI
is
made
available. The extra byte may
be
used to detect that a byte was dropped
on.the
HP-IB, or it
can
be
used to determine the
end
of a transfer without maintaining a byte
count. Finally,
the
bus
controller issues
an
Untalk
and
the sequence
is
complete.
Sequences
other
than
the
ones
shown may, in
some
cases, work;
but
there is
no
guarantee
that they
will
be
compatible with
other
HP-IB discs or with
futur~
HP disc memories.
The controller only operates
on
a single
command
at
any given time; i.e., overlapped
operations
on
multiple drives
are
not possible.
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