INPUT
/
OUTPUT
5T
ATU5
INDICATORS
(Cont'd)
Condition Code
Input/Output Operation
by, and stored in, the device control electronics until a Sense conlmand is
issued.
At
that
time the
status
information (Sense bytes)
are
transferred
to main memory similar to a data transfer.
• The condition code is set by
the
input/output
instructions and can be
tested by
the
Branch
On
Condition instruction.
It
should be noted
that
the
condition code settings indicate the result of the
input/output
instructions
only. They
do
not indicate the results of the
input/output
operation. Con-
dition Code settings
for
all
input/output
instructions
are
as follows:
Start Device Instruction Condition Code SeHings
Condition
I/O
Operation
Code Initiated
o Yes
1
No
(Cont'd)
Meaning
1. The device control electronics
and
the
device specified
are
available.
2.
The
Start
Device
instruction
specifies a Sense com-
mand
to
a device
that
is inoperable.
This condition code indicates
that
either
the
channel
status
byte
or
the
standard
device
byte
has
been
stored
in
the
channel
registers
for
the
specified channel.
The channel
status
byte
is
stored
under
the
following
conditions:
1.
A
parity
error
occurs while accessing
the
Channel
Address Word, Channel Block Address,
or
a Channel
Command Word. The channel control check
bit
in
the
channel
status
byte
is
set.
2.
The Memory
Protect
feature
is
not
installed
and
the
key
in
the
CAW
is
not
zero. The
program
check
bit
in
the
channel
status
byte
is set.
3.
The
main
memory
address
specified
in
the
CAW is
not
on a double
word
boundary. The
program
check
bit
in
the
channel
status
byte
is
set.
4.
The
main
memory
address
in
the
CCW specifies
an
address
outside
the
available
memory
for
the
system.
The
program
check
bit
in
the
channel
status
byte
is set.
The
standard
device
byte
is
stored
under
the
following
conditions:
61
1.
The specified device control electronics on
the
multi-
plexor
channel indicates
that
a device
request
inter-
rupt
pending condition is
present.
The
external
device
request
interrupt
pending
bit
in
the
standard
device
byte
is set.
2.
The
Start
Device
instruction
specifies a
command
which
is
other
than
a Sense command
and
the
addressed device
is
inoperable. The device inoperable
bit
in
the
standard
device
byte
is
set.
3.
The
specified device is
busy
but
the
device control
electronics
is
not
busy
(Le.,
tape
rewinding, off-line
seek to a
random
access device). The device
busy
bit
and
the
device end
bit
in
the
standard
device
byte
is
set.
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