Block 9
(Cont'd)
Test Device
Instruction
Input/Output
Operation
2.
The
standard
device byte is
not
stored
if
the
condition codes
are
0, 2, 3.
3.
If
an
interrupt
pending
(termination
or
external
device request)
condition exists on a specified selector channel, the condition code
is
set
to zero.
4.
The channel
and
device
are
terminated
at
the
next
data
service
request (see Servicing a
Data
Transfer).
5.
The Channel Address Word (
CAW),
Channel Block Address
(CBA),
and
Channel Command Word (CCW)
are
not used
by
this
instruction.
6.
If
execution
of
this
instruction causes
the
standard
device byte to
be stored in
the
multiplexor channel registers,
the
program
must
inhibit
interrupts
from
the
multiplexor channel until
the
standard
device byte
has
been analyzed
or
moved
from
the
channel registers.
If
interrupts
are
permitted
and
one occurs,
the
standard
device
byte is destroyed .
• The
status
of
an
input/output
device can be tested
by
executing a
Test
Device instruction. The
Test
Device
instruction
is a privileged operation
and
can be executed only
if
the
mode
bit
(bit
position 15 of
the
Interrupt
Status
register
for
the
current
state)
is
set
to
0.
This
instruction
is exe-
cuted in
the
normal mode. Continuation
of
program
execution is delayed
until
the
instruction is terminated.
Both
the
channel
number
and
the
device
number
must
be specified
in
the instruction. Because
the
Channel Address Word is
not
referred
to by
the
Test Device instruction,
the
Channel Address Word, Channel Block
Address,
and
a Channel Command Word
are
not
required.
Upon execution
of
a
Test
Device instruction,
the
following events occur
(see figure
7).
Block
1 •
If
the privileged mode
bit
(bit
position 15
of
the
Interrupt
Status
register)
for
the
current
state
is
not
set
to
0,
the
privileged operation
bit
is
set
in
the
Interrupt
Flag
register
and
an
interrupt
occurs,
if
permitted.
Block 2 •
If
the
specified channel is a selector channel
that
is
not
available on
the
system,
the
condition code is
set
to 3,
the
Test Device
instruction
is
terminated
and
program
control is
transferred
to
the
next
instruction.
Block 3 •
If
the
specified channel is a selector channel
that
is
busy
or
has
on
interrupt
pending (termination
or
external
device request) ;
or
if
the
speci-
fied
channel is
the
multiplexor
that
is
operating
in the
burst
mode,
the
condition code is
set
to
2,
the
Test
Device instruction is
terminated
and
program
control is
transferred
to
the
next
instruction.
Block
4.
• The channel
status
byte
and
the
standard
device
byte
for
the
specified
channel
are
reset
to zeros
in
the
appropriate
channel registers.
Block 5 • The device address
as
specified in
the
Test
Device
instruction
is
sent
to all
trunks
on
the
addressed channel.
56
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