The
which the channel is configured performs a program
reset, initial-program reset, system-clear reset, or
power-on reset, when a power-on sequence is per
formed by the channel, and, under certain condi
tions, when a channel detects equipment malfunc
tions.
operations on all subchannels.
and all interruption conditions in all subchannels are
reset, and all operational subchannels are placed in
the available state. The channel signals system reset
to all
The
nels when they detect certain equipment malfunc
tions.
selective reset to the device that is connected to the
channel at the time the malfunction is detected. No
subchannels are reset.
Effect of Reset on a Working Device
If the device is currently communicating over the
from the channel. Data transfer and any operation
using the facilities of the control unit are immediate
ly concluded, and the
positioned at the beginning of a block. Mechanical
motion not involving the use of the control unit,
such as rewinding magnetic tape or positioning a
disk-access mechanism, proceeds to the normal
stopping point, if possible. The device appears in the
working state until the termination of mechanical
motion or the inherent cycle of operation, if any,
whereupon it becomes available.
in the device and control unit is reset, but an inter
ruption condition may be generated upon completing
any mechanical operation.
Reset Upon Malfunction
The type of reset executed in the channel depends
on the type of malfunction and the channel. When a
reset occurs upon malfunction, the program is alert
ed by an interruption or, when the malfunction is
detected during the execution of an
by the setting of the condition code. In either case
the
dressed by the
device that is reset. In channels sharing equipment
with the
nel may be indicated by a machine-check interrup
tion, which mayor may not be followed by an
a
The method of identifying malfunctions depends on
the model.
Condition Code
The results of certain tests by the channel and de
vice, and the original state of the addressed part of
the
the
execution of the instruction is concluded, that is, the
time the
instruction. The condition code ordinarily indicates
whether or not the channel has performed the in
struction and, if not, the reason for the rejection. In
the case of
independently of the device, a condition code
be set that is later superseded by a deferred condi
tion code stored in the
operations following an operation that sets the con
dition code use the code for decision-making.
The following table lists the conditions identified
and the corresponding condition codes for each
ated abbreviations were previously defined in
the table represent the decimal value of the code.
The instructions
state, depending on the type of operation initiated.
Equipment malfunctions and programming errors
generally cause condition code 1 to be set and the
The available condition is indicated only when no
errors are detected during the execution of the
When a subchannel on the multiplexer channel
contains a pending interruption condition (state
AIX), the
operation normally is in the interruption-pending
state. When the channel detects during the execu
tion of
condition code 3 is set. Similarly, condition code 3 is
set when HALT
dressed to a sub channel in the working state (state
AWX), but the device turns out to be not operation
al.
Error conditions, including all equipment or pro
gramming errors detected by the channel or the
erally cause the
however, a channel equipment error may cause a
machine-check interruption but no
to occur, with no storing of the
