the addressed device or is working with the
addressed device. The protection-key,
command-address, and count fields describe
the state of the operation at the time CLEARI/O is executed. (Some channels alternatively
indicate busy under these conditions.)
4. The channel detected an equipment error dur
ing the execution of the instruction. The CSW
identifies the error condition. The states of the
channel and theI/O operations in progress are
unpredictable. The limited channel logout, if
stored, indicates a sequence code of000. When CLEAR I/O cannot be executed because
of a pending-logout condition that affects the opera
tional capability of the channel, a full CSW is stored.
The fields in the CSW are all set to zeros, with the
exception of the logout-pending and channel-control
check bits, which are set to ones. No channel logout
is associated with this status.
Program Exceptions:
Privileged operation
Resulting Condition Code:a No operation in progress for the
addressed device
1 CSW stored
2 Channel busy
3 Not operational
The condition code set by theCLRIO function
for all possible states of theI/O system is shown
graphically as follows. The condition code set when
CLEARI/O causes the TIO function to be per
formed is shown graphically in the definition of the
instruction TESTI/O. Channel A
Programming Note
Since some channels cause a condition code 2 to be
set when the instruction is received and the channel
is in the working state, it may be useful to issue a
halt instruction and then CLEARI/O to the desired
address.Using HALT DEVICE will ensure that
condition code 2 is received on the CLEARI/O only when the channel is working with a device oth
er than the one addressed.U sing HALT I/O will
ensure that the current working state, if any, is termi
nated without regard for the address.
Because of the inability of CLEARI/O to termi
nate operations on some channels when in the work
ing state, the instruction is not a suitable substitute
for HALTI/O or HALT DEVICE.
The combination of HALT DEVICE followed by
CLEARI/O can be used to clear out all activity on
a channel by executing the two instructions for all
device addresses on the channel.
Halt Device
HDV D2(B2) [S]
9E01 82 D20 16 20 31
The currentI/O operation at the addressed I/O device is terminated. The subsequent state of the
sub channel depends on the type of channel. HALT
DEVICE is executed only when theCPU is in the
supervisor state. Bits 8-14 of the instruction are
ignored.Wf I Subchannel 1 A Ilf 1
1
# 1 WfIW# 1 N
o0 1* 0 1* 3
AIlf 1 1# I Wf I W#I N
o0 1* 0 1* 3
AIlf 1
1
# t t tt t tt ttt A
W
NAvailable I nterruption pending If = I nterruption pending for a device other than
the one addressed1#= Interruption pe.nding for the addressed device
WorkingWf = Working with a device other than the one
addressed
W#= Working with the addressed device
Notoperational CSW stored
Condition CodesSet by CLEAR I/O t In the WfAX, WflfX, and W#Nf.X states, a
condition code0 or 2 may be set, depending on the channel. tt In the Wfl#X, W#N#X, and W#XX states, a
condition code 1 (with theCSW stored) or 2 may be set,
depending on thechannel. ttt In the WfNX state, a condition code 2 or 3 may be set,
depending on thechannel. Note: Underscored codes pertain to conditions that can occur only on the multiplexer channel. lnput/Output Operations 199
addressed device. The protection-key,
command-address, and count fields describe
the state of the operation at the time CLEAR
indicate busy under these conditions.)
4. The channel detected an equipment error dur
ing the execution of the instruction. The CSW
identifies the error condition. The states of the
channel and the
unpredictable. The limited channel logout, if
stored, indicates a sequence code of
of a pending-logout condition that affects the opera
tional capability of the channel, a full CSW is stored.
The fields in the CSW are all set to zeros, with the
exception of the logout-pending and channel-control
check bits, which are set to ones. No channel logout
is associated with this status.
Program Exceptions:
Privileged operation
Resulting Condition Code:
addressed device
1 CSW stored
2 Channel busy
3 Not operational
The condition code set by the
for all possible states of the
graphically as follows. The condition code set when
CLEAR
formed is shown graphically in the definition of the
instruction TEST
Programming Note
Since some channels cause a condition code 2 to be
set when the instruction is received and the channel
is in the working state, it may be useful to issue a
halt instruction and then CLEAR
address.
condition code 2 is received on the CLEAR
er than the one addressed.
ensure that the current working state, if any, is termi
nated without regard for the address.
Because of the inability of CLEAR
nate operations on some channels when in the work
ing state, the instruction is not a suitable substitute
for HALT
The combination of HALT DEVICE followed by
CLEAR
a channel by executing the two instructions for all
device addresses on the channel.
Halt Device
HDV D2(B2) [S]
9E01 82 D2
The current
sub channel depends on the type of channel. HALT
DEVICE is executed only when the
supervisor state. Bits 8-14 of the instruction are
ignored.
1
#
o
A
o
A
1
#
W
N
the one addressed
Working
addressed
W#= Working with the addressed device
Not
Condition Codes
condition code
condition code 1 (with the
depending on the
depending on the