address can occur in the channel because the program
has specified an invalid address in the ccw or because
the channel has stepped the address above the highest
available address or, on reading backward, below zero.
Invalid Key: The CAW contains a nonzero storage
protection key in a model not having the protection
feature installed.
Invalid CAW Format: The CAW does not contain
zeros in bit positions 4-7.
Invalid CCW Format: A ccw other than a ccw spe
cifying transfer in channel does not contain zeros in
hit positions 37-39.
Invalid Sequence: The first ccw designated by the
CAW specifies transfer in channel or the channel has
fetched two successive ccw's both of which specify
transfer in channel.
Detection of the program-check condition during
the initiation of an operation causes execution of the
operation to be suppressed. When the condition is de
tected after the device has been started, the device is
signaled to terminate the operation. The program
check condition causes command chaining to be sup
pressed.
ProtectionCheck Protection check occurs when the channel attempts to
place data in a portion of main storage that is protect
ed for the current operation on the subchannel. The
protection key associated with theI/O operation does
not match the key of the addressed main-storage lo
cation, and neither of the keys is zero.
Detection of the protection-check condition causes
the device to be signaled to terminate the operation;
command chaining is suppressed.
The protection-check condition can be generated
only on models having the protection feature installed.
Channel DataCheck Channel data check is caused by data errors detected
in the channel or in main storage. The condition covers
all data transferred to or from anI/O device, including
sense and control information. It includes any parity
errors detected onI/O data in main storage, in the
channel, or as received from the device over theI/O interface.
The channel attempts to force correct parity on data
placed in main storage.On output operations, the par
ity of data sent to the device is not changed.Parity errors on data cause command chaining to be
suppressed and, depending on model, may cause the
current operation to be terminated. When the channel
and theCPU share common equipment, parity errors on
data may cause malfunction reset to be performed. The
recovery procedure in the channel and the subsequent
state of the subchannel upon a malfunction reset de
pend on the model.
Channel ControlCheck Channel control check is caused by any machine mal
functioning affecting channel controls. The condition
includes parity errors on ccw and data addresses and
parity errors on the contents of the ccw. Conditions
responsible for channel control check usually cause the
contents of the csw to be invalid and conflicting.
The csw as generated by the channel has correct
parity. The channel either forces correct parity on the
csw fields or sets the invalid fields to zero.
Detection of the channel-control-check condition
causes the current operation, if any, to be immediately
terminated and may cause the channel to perform the
malfunction-reset function. The recovery procedure in
the channel and the subsequent state of the subchannel
upon a malfunction reset depend upon the model.
Interface ControlCheck Interface control check is caused by any invalid signal
on theI/O interface. The condition is detected by the
channel and usually indicates malfunctioning of anI/O device. It can be due to the following reasons:
1. The address or status byte received from a de
vice has invalid parity.
2. A device responded with an address other than
the address specified by the channel during initiation
of an operation.
3. During command chaining the device appeared
not operational or indicated the busy condition with
out providing any other status bits.
4. A signal from a device occurred at an invalid
time or had invalid duration.Detection· of the interface-control-check condition
causes the current operation, if any, to be immediately
terminated and may cause the channel to perform the
maHunction-reset function. The recovery procedure in
the channel and the subsequent state of the subchan
nel upon a malfunction reset depends on the model.
ChainingCheck Chaining check is caused by channel overrun during
data chaining on input operations. The condition oc
curs when theI/O data rate is too high for the particu
lar resolution of data addresses. Chaining check cannot
occur on output operations.
Detection of the chaining-check condition causes the110 device to be signaled to terminate the operation.
It causes command chaining to be suppressed.
Input/Output Operations 113
has specified an invalid address in the ccw or because
the channel has stepped the address above the highest
available address or, on reading backward, below zero.
Invalid Key: The CAW contains a nonzero storage
protection key in a model not having the protection
feature installed.
Invalid CAW Format: The CAW does not contain
zeros in bit positions 4-7.
Invalid CCW Format: A ccw other than a ccw spe
cifying transfer in channel does not contain zeros in
hit positions 37-39.
Invalid Sequence: The first ccw designated by the
CAW specifies transfer in channel or the channel has
fetched two successive ccw's both of which specify
transfer in channel.
Detection of the program-check condition during
the initiation of an operation causes execution of the
operation to be suppressed. When the condition is de
tected after the device has been started, the device is
signaled to terminate the operation. The program
check condition causes command chaining to be sup
pressed.
Protection
place data in a portion of main storage that is protect
ed for the current operation on the subchannel. The
protection key associated with the
not match the key of the addressed main-storage lo
cation, and neither of the keys is zero.
Detection of the protection-check condition causes
the device to be signaled to terminate the operation;
command chaining is suppressed.
The protection-check condition can be generated
only on models having the protection feature installed.
Channel Data
in the channel or in main storage. The condition covers
all data transferred to or from an
sense and control information. It includes any parity
errors detected on
channel, or as received from the device over the
The channel attempts to force correct parity on data
placed in main storage.
ity of data sent to the device is not changed.
suppressed and, depending on model, may cause the
current operation to be terminated. When the channel
and the
data may cause malfunction reset to be performed. The
recovery procedure in the channel and the subsequent
state of the subchannel upon a malfunction reset de
pend on the model.
Channel Control
functioning affecting channel controls. The condition
includes parity errors on ccw and data addresses and
parity errors on the contents of the ccw. Conditions
responsible for channel control check usually cause the
contents of the csw to be invalid and conflicting.
The csw as generated by the channel has correct
parity. The channel either forces correct parity on the
csw fields or sets the invalid fields to zero.
Detection of the channel-control-check condition
causes the current operation, if any, to be immediately
terminated and may cause the channel to perform the
malfunction-reset function. The recovery procedure in
the channel and the subsequent state of the subchannel
upon a malfunction reset depend upon the model.
Interface Control
on the
channel and usually indicates malfunctioning of an
1. The address or status byte received from a de
vice has invalid parity.
2. A device responded with an address other than
the address specified by the channel during initiation
of an operation.
3. During command chaining the device appeared
not operational or indicated the busy condition with
out providing any other status bits.
4. A signal from a device occurred at an invalid
time or had invalid duration.
causes the current operation, if any, to be immediately
terminated and may cause the channel to perform the
maHunction-reset function. The recovery procedure in
the channel and the subsequent state of the subchan
nel upon a malfunction reset depends on the model.
Chaining
data chaining on input operations. The condition oc
curs when the
lar resolution of data addresses. Chaining check cannot
occur on output operations.
Detection of the chaining-check condition causes the
It causes command chaining to be suppressed.
Input/Output Operations 113