Bits 16-31 of the second-operand address identify
the channel, the subchannel, and the 110 device to
which instruction applies.
When the channel is either available or in the
interruption pending state with the subchannel avail­
able or working with the addressed device, HALT
DEVICE causes the addressed device to be selected
and to signaled to terminate the current opera­
tion, if any. If the subchannel is working with the
addressed device, HALT DEVICE also causes the
subchannel to be set up to signal termination of the
device operation the next time the device requests or
offers a byte of data, if any. Chaining, if indkated in
the subchannel, is suppressed. If the sub channel is
available, the sub channel is not affected.
When the channel is either available or in the
interruption pending state with the sub channel either
working with a device other than the one addressed
or in the interruption pending state, no action is tak­
en.
When the channel is working in burst mode with
the addressed device, data transfer across the 1/0 interface for the operation is immediately tenninat­
ed, and the device immediately disconnects from the
channel. Chaining, if indicated in the subcharmel, is
suppressed.
When the channel is working in burst mode with a
device other than the one addressed, and the sub­
channel is available, in the interruption pending
state, or working with a device other than the; one
addressed, no action is taken. If the sub channel is
working with the addressed device, the sub channel is
set up to signal termination of the device operation
the next time the device requests or offers a byte of
data, if any. Chaining, if indicated in the subchannel,
is suppressed.
When the channel is working in burst mode with a
device other than the one addressed and the sub­
channel is not operational, is in the interruption
pending state, or is working with a device other than
the one addressed, the resulting condition code may,
in some channels, be determined by the sub channel
state.
Termination of a burst operation by HALT DE­
VICE on a selector channel causes the channel and
sub channel to be placed in the interruption pending
state. Generation of the interruption condition is not
contingent on the receipt of a status byte from the
device. When HALT DEVICE causes a burst opera­
tion on a byte-multiplexer channel to be terminated,
the sub channel associated with the burst operation
remains in the working state until the device pro­
vides ending status, whereupon the subchannel en­
ters the interruption pending state. The termination
of a burst operation by HALT DEVICE on a block- 200 System/370 Principles of Operation multiplexer channel may, depending on the model
and the type of subchannel, take place as for a selec­
tor channel or may allow the sub channel to remain
in the working state until the device provides ending
status.
When any of the three conditions numbered be­
low occurs, HALT DEVICE causes the 16-bit unit­
and channel-status portion of the CSW to be re­
placed by a new set of status bits. The contents of
the other fields of the CSW are not changed. The CSW stored by HALT DEVICE pertains only to the
execution of HALT DEVICE and does not describe
under what conditions the 110 operation at the ad­
dressed subchannel is terminated. The extent of data
transfer, and the conditions at the termination of the
operation at the subchannel, are provided in the CSW associated with the interruption condition
caused by the termination. The three conditions are:
1. The addressed device is selected and signaled
to terminate the current operation, if any. The CSW then contains zeros in the status field
unless a machine malfunction is detected.
2. The control unit is busy and the device cannot
be given the signal to temrinate the operation.
The CSW unit-status field contains the busy
and status modifier bits. The channel-status
field contains zeros unless a machine malfunc­
tion is detected.
3. The channel detects a machine malfunction
during the execution of HALT DEVICE. The
status bits in the CSW then identify the error
condition. The state of the channel and the
progress of the 110 operation are unpredicta­
ble.
When HALT DEVICE cannot be executed be­
cause of a pending logout condition which affects
the operational capability of the channel or subchan­
nel, a full CSW is stored. The fields in the CSW are
all set to zeros, with the exception of the logout­
pending bit and the channel control check bit, which
are set to ones. No channel logout is associated with
this status.
When HALT DEVICE causes data transfer over
the 110 interface to be terminated, the control unit
associated with the operation remains unavailable
until the data-handling portion of the operation in
the control unit is concluded. Concluding of this
portion of the operation is signaled by the generation
of channel end. This may occur at the normal time
for the operation, or earlier, or later, depending on
the operation and type of device. If the control unit
is shared, all devices attached to the control unit
appear in the working state on that channel until the
channel end condition is accepted by the CPU. The 110 device executing the terminated operation re-
mains in the working state until the end of the inher­
ent cycle of the operation, at which time device end
is generated. If blocks of data at the device are de­
fined, as in read-type operations on magnetic tape,
the recording medium is advanced to the beginning
of the next block.
When HALT DEVICE is issued at a time when
the subchannel is available and no burst operation is
in progress, the effect of the HALT DEVICE signal
depends partially on the type of device and its state.
In all cases, the HALT DEVICE signal has no effect
on devices that are not in the working state or are
executing a mechanical operation in which data is
not transferred across the I/O interface, such as
rewinding tape or positioning a disk access mecha­
nism. If the device is executing a type of operation
that is unpredictable in duration, or in which data is
transferred across the I/O interface, the device in­
terprets the signal as one to terminate the operation.
Pending attention or device end conditions at the devke are not reset.
Program Exceptions:
Privileged operation
Resulting Condition Code:
o Subchannel busy with another device
or interruption pending
1 CSW stored
2 Channel working
3 Not operational
The condition code set by HALT DEVICE for all
possible states of the I/O system is shown graphical- Channel A Subchannel A II W# Q Q
A
ly. See "States of the Input/Output System" for a
detailed definition of the A, I, W, and N states.
Programming Note
Some selector and byte-multiplexer channels de­
signed prior to the defining of HALT DEVICE (for
example, the 2860), will execute HALT DEVICE as
HALT I/O. A program can ensure complete com­
patibility between HALT DEVICE and HALT I/O on such channels by observing the following conven­
tions:
1. On a byte-multiplexer channel, do not issue
HALT DEVICE to a multiplexing device when
a burst operation is in progress on the channel.
2. On a byte-multiplexer channel, do not issue
HALT DEVICE to a device on a shared sub­
channel while that subchannel is working with
a device other than the one addressed.
3. On a selector channel in the working state, do
not issue HALT DEVICE to any device other
than the one with which the channel is work­
ing.
The execution of HALT DEVICE always causes
data transfer across the I/O interface for the ad­
dressed device to be terminated. The condition code
and the CSW (when stored) indicate whether the
control unit was signaled to terminate its operation
during the execution of the instruction. If the control
unit was not signaled to terminate its operation, the
condition code and the CSW (when stored) imply
the conditions under which the execution of a HALT
DEVICE for the same address will cause the control
unit to be signaled to terminate.
W#
P Q 1. .:!: + ! Control Unit
- Device I A ,I ,WIN I IA I I ,WIN I IA III
W
IN, I AI11W IN I A
W
N
*
1* 1* 1* 3 Available Interruption pending
Working
1* 1* 1* 3
- W=I= = Working with a device other than the
one addressed W# = Working with the addressed device
Not operational CSW stored
Condition Codes Set by HALT DEVICE
1* 1* 1* 3
@ In the W#XX state, either condition code 1 (with CSW stored) or
condition c'ode 2 may be set, depending on the channel and the
conditions in the channel. Condition code 1 (with CSW stored) can be
set only if the control unit has received the signal to terminate.
+ In the W=I=IX and W=I=W=I=X states, either condition code 0 or 2 may be
set, depending on the channel and the conditions in the channel. $ In the state, either condition code 2 or 3 may be set, depending
on the channel type and system model. Note: Underscored condition codes pertain to conditions that can occur only on the multiplexer channel. Input/Output Operations 201
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