o 8 31
5
D
32
A sense operation
to transfer data from the device to
storage. The data
in an ascending order of addresses,
starting with the address specified in
the
command
from sense indicators rather than from a
record source.
The basic sense command (modifier bits
set to zeros) initiates
tion on all
retrieval of up to 32 bytes of data.
The basic sense command does not
of sense indicators. The basic sense
command sent to an addressable control
unit is accepted even though the
addressed
state. If the control unit detects an
error during the sense operation, unit
check
status condition.
The purpose of the basic sense command
is to provide data detailed enough to
ascertain the actual state of the device
and unusual conditions associated with
the execution of the
during which the error was detected.
The first six bits of the first sense
data byte (sense byte
the basic sense command are common to
all
to ones, designate the following:
Bit Designation
1 Intervention required
2 Bus-out check
4 Data check
5
first six bits:
Command Reject:
ward issued to a direct-access-storage
device, or which the device cannot
execute because of its present state,
such as
when the program issues an invalid
sequence of commands, such as write to
previous designation of the block.
when invalid data is transferred and the
data is treated as an extension of the
command. For example, command reject is
storage device.
Intervention Required: The last opera
tion could not
vention at the device. This bit indi
cates situations such as the hopper in a
card punch being empty or the printer
being out of paper. It is also turned
on when the addressed device is not
ready, is in test mode, or is not
provided on the control unit.
control unit has received a data byte or
a command code with an invalid parity
from the channel. During writing, bus
out check indicates that incorrect data
may have been recorded at the device,
but this does not cause the operation to
be terminated prematurely. Parity
errors on command codes and control
information cause the operation to
checking for situations that would cause
command reject and intervention
required.
Equipment
tion, the device or the control unit has
detected equipment malfunctioning, such
as an invalid card-hole count or
Data
unit
than those included in bus-out check.
Data check identifies errors associated
with the recording medium and includes
errors such as reading an invalid card
code or detecting invalid parity on data
recorded on magnetic tape.
cates that incorrect data may have been
placed in storage. The control unit
forces correct parity on data sent to
the channel.
indicates that incorrect data may have
been recorded at the device. Unless the
operation is of
precludes meaningful continuation, data
errors on reading and writing do not
cause the operation to be terminated
prematurely.