Invalid IDAW Address: The channel has
attempted to fetch an IDAW from a stor­
age location which is not available to
the channel. An invalid IDAW address
can occur in the channel because the
program has specified an invalid address
in a CCW that specifies indirect data
addressing or because the channel, on
sequentially fetching IDAWs, has
attempted to fetch from an unavailable
location.
Invalid Data Address: The channel has
attempted to transfer data- to or from a
storage location which is not available
to the channel. An invalid data address
can occur in the channel because the
program has specified an invalid address
in the CCW, or in an IDAW, or because
the channel, on sequentially accessing
storage, has attempted to access an
unavailable location.
Invalid IDAW Specification: The 24-
bit-IDAW facility is installed and bits 0-7 of the IDAW are not all zeros, or
the second or subsequent IDAW does not
specify the first or, for read-backward
operations, the last byte of a 2K-byte
storage block. The 31-bit IDAW facility
is installed and bit 0 of the IDAW is
not zero, or the second or subsequent
IDAW does not specify the first or, for
read-backward operations, the last byte
of a 2K-byte storage block.
Invalid CAW Format: The CAW does not
contain zeros in bit positions 4-7 when
the suspend-and-resume facility is not
provided by the system model or in bit
positions 5-7 when the suspend-and­
resume facility is provided.
Invalid CCW Format: A CCW other than a CCW specifying transfer in channel does
not contain zeros in bit positions 38-39
when the suspend function is not
provided for the subchannel or does not
contain zero in bit position 39 when the
suspend function is provided.
Invalid Suspend Flag: A CCW fetched
during data chaining, other than a CCW specifying transfer in channel, does not
contain a zero in bit position 38. A CCW other than a CCW specifying transfer
in channel does not contain a zero in
bit position 38 and either suspend
control was not specified in the CAW, or
the suspend function is not operable for
the subchannel.
Invalid Sequence: The first CCW desig­
nated by the CAW specifies transfer in
channel, or the channel has fetched two
successive CCWs both of which specify
transfer in channel, or a sequence of
256 or more CCWs with command chaining
specified were executed by the channel
and did not result in the transfer of
any data with an I/O device.
Detection of program check during the
initiation of an operation causes
execution of the operation to be
suppressed. When program check is
detected after the operation has been
initiated at the device, the device is signaled to conclude the operation the
next time it requests or offers a byte
of data. Program check causes command
chaining and command retry to be
suppressed.
Protection Check Protection check occurs when the channel
attempts a storage access that is
prohibited by key-controlled storage
protection. Protection applies to the
fetching of CCWs, IDAWs, and output
data, and to the storing of input data.
Storage accesses associated with each
channel program are performed using the
subchannel key provided in the CAW asso­
ciated with that channel program. For
details, see the section "Key-Controlled
Protection" in Chapter 3, "Storage."
When protection check occurs during the fetching of a CCW that specifies the initiation of an I/O operation, or
occurs during the fetching of the first
IDAW, the operation is not initiated. When protection check is detected after
the operation has been initiated at the
device, the device is signaled to
conclude the operation the next time it requests or offers a byte of data.
Protection check causes command chaining
and command retry to be suppressed. Channel-Data Check Channel-data check indicates that a
machine error has been detected in the
information transferred to or from stor­
age during an I/O operation, or that an
error has been detected on data trans­
ferred from the device during an input
operation. This information includes
the data read or written, as well as the information transferred as data during a sense or control operation. The error
may have been detected in the channel, in storage, or on the path between the
two. Channel-data check may be indi­
cated for data with an invalid
checking-block code in storage when the
data is referred to by the channel but the data does not participate in the
operation. This can happen, for
example, on an input operation when less
than a full checking block of data is to
be placed in storage. In this case,
called a partial store, the entire
checking block is fetched from storage,
is updated with the input data, and is
replaced in storage. If a CBC error is
detected when the checking block is fetched, it cannot be corrected because
only part of the checking - block is cnapter 13. Input/Output Operations 13-71

updated during a partial store. In this situation, a channel-data check condi­
tion is recognized because of a CBC error in data referred to (the original contents of the checking block> and not
because of an error in the input data itself. Whenever an error on input data is indi­
cated by means of channel-data check,
the channel forces correct parity on all
data received from the I/O device, and
all data placed in storage has valid
checking-block code. When, on an input
operation, the channel attempts to store
less than a complete checking block, and
when invalid checking-block code is
detected on the checking block in stor­
age, the contents of the location remain
unchanged with invalid checking-block
code. On an output operation, whenever
a channel-data check is indicated, all
bytes that came from a checking block
with invalid checking-block code have
been transmitted with parity errors.
Channel-data check causes command chain­
ing and command retry to be suppressed
but does not affect the execution of the
current operation. Data transfer
proceeds to normal completion, if possi­
ble, and an interruption condition is generated when the device presents chan­
nel end. A logout may be performed,
depending on the channel. Accordingly,
the detection of the error may affect
the state of the channel and the device.
Channel-Control Check
Channel-control check is caused by
machine malfunction affecting channel
controls. It may be caused by invalid
checking-block codes on CCW addresses,
data addresses, and the contents of the
CCW. Channel-control check may also
include those channel-detected errors
associated with data transfer that are
not indicated as channel-data check, as
well as those communication errors
detected by the channel that are not
indicated as interface-control check.
Errors responsible for channel-control
check may cause the contents of the CSW to be invalid and conflicting. The CSW as generated by the channel has valid
checking-block code.
Detection of channel-control check caus­
es the current operation, if any, to be immediately concluded.
Channel-control check is set whenever CSW bit 5, logout pending, is set to
one.
In some situations, machine malfunctions
affecting channel control may instead be reported as an external-damage or system-damage machine-check condition.
13-72 System/370 Principles of Operation Interface-Control Check
Interface-control check indicates that
an invalid signal has been received by
the channel when communicating with a
control unit or device. This check is
detected by the channel and usually
indicates malfunctioning of an I/O device. It can be due to the following:
1. The device address or status byte
received from a device has invalid
parity.
2. A device responded with a device
address other than the device
address specified by the channel
during initiation of an operation.
3. During command chaining or command
retry the device appeared not oper­
ational.
4. A signal from a device occurred at
an invalid time or had invalid
duration.
5. A device signaled I/O-error alert.
The interface-control-check condition
may also include those channel-detected
errors associated with data transferred
from the device that are not indicated
as channel-data check.
Detection of interface-control check
causes the current operation, if any, to
be immediately concluded.
Chaining Check
Chaining check is caused by channel
overrun during data chaining on input
operations. Chaining check occurs when
the I/O data rate is too high to be
handled by the channel and by storage
under current conditions. Chaining
check cannot occur on output operations.
Chaining check causes the I/O device to
be signaled to conclude the operation.
It causes command chaining and command
retry to be suppressed. CONTENTS OF CHANNEL-STATUS WORD The contents of the CSW depend on the
reason the CSW was stored and on the programming method by which the informa­
tion is obtained. The deferred­
condition-code field and the status
portion identify the reason the CSW was
stored. The subchannel-key, suspended­
indication, logout-pending, deferred-