Input/Output Operation
Block 3 •
If
the specified channel is a selector channel
that
is busy
or
has
an
interrupt
pending (termination
or
external device r,equest)
or
if
the speci-
fied
channel is
the
multiplexor
that
is operating in
the
burst
mode,
the
con-
dItion code is
set
to
2,
the
Start
Device instruction is terminated and
program
control is
transferred
to the next instruction. The
input/output
operation is not initiated.
Block
4-
•
The
channel
status
byte
and
the
standard
device byte
fO'r
the
specified
channel
are
reset to
zerO's
in the appropriate channel registers.
Block 5 •
If
the Memory Protect
feature
is not installed,
the
key in the Channel
Address Word (CAW) is tested to see
if
it
is equal
to
zeros.
If
it
is
nO't
zeros, the
program
check
bit
in
the
channel
status
byte is set,
the
condition
code is
set
to'
1, the
Start
Device instruction is terminated,
and
program
control is
transferred
to
the
next instruction.
The
input/output
operation
is not initiated.
Block 6 • The main memory address in
the
Channel Address Word is tested
to
see
if
it
is on a double word boundary.
If
it
is not,
the
prO'gram check
bit
in
the
channel
status
byte is set,
the
conditiO'n code is
set
to
1,
the
Start
Device instruction is terminated and
program
contrO'I
is
transferred
to
the
next instruction. The
input/output
operation is not initiated.
Block 7 • The main memory address in the Channel
CO'mmand
WO'rd
(CCW) is
tested to see
if
it
is within the available main memory
for
the
system.
If
it
is not, the prO'gram check
bit
in
the
channel
status
byte is set,
the
condi-
tion code is set
to'
1,
the
Start
Device instruction is terminated
and
program
control is
transferred
to
the
next instruction. The
input/output
operation
is not initiated.
Block 8 •
If
the specified channel is the multiplexor channel,
the
command
cO'de
in
the
Channel Command Word is tested to see
if
a
burst
mode operation
has
been specified.
Block 9 •
If
a
burst
mO'de
operation has been specified, a
test
is made to see
if
there
is a
terminating
interrupt
pending on
any
of
the
trunks
on
the
multi-
plexor.
If
a
terminating
interrupt
is pending,
the
condition code is
set
to'
2,
the
Start
Device instruction is terminated
and
program
control is
trans-
ferred
to
the
next instruction. The
input/output
operation is
not
initiated.
Block
10
• The device address
as
specified in the
Start
Device instruction is
sent
to all
trunks
on
the
addressed channel.
Block
11
• A
test
is made to see
if
the specified device cO'ntrol electronics is oper-
able. The device control electronics has
50
micrO'seconds
to
signal
the
processor
that
it
is O'perable.
If
it
dO'es
not,
the
cO'ndition code is set
to
3,
the
Start
Device instruction is terminated and
program
control is
trans-
ferred
to
the
next instruction. The
input/output
operatiO'n is not initiated.
Block
12
•
If
the specified device
cO'ntrol
electronics is operable,
the
cO'mmand
code from the Channel Command Word is
sent
to'
the
specified device
control electronics.
50
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