ferred from the selected control unit. This sense data
may be one or more bytes long. It provides detailed
information concerning the selectedI/O device, such
as a stacker-full condition of a card reader or a fiIe
protected condition of a reel of magnetic tape on a
tape unit.Sense data have a significance peculiar to
theI/O device involved.
TransferIn Channel
The transfer-in-channel command specifies the loca
tion of the next ccw to be used by the channel when
ever the programmer desires to break the existing
chain of ccw's and cause the channel to begin fetch
ing a new chain of ccw's from a different area in
main storage.
External documents, such as punched cards or mag
netic tape, may carry ccw's that the channel can use
to govern reading of the external document being
read.Input / Output Termination
Input/output operations normally terminate with de
vice-end signal and channel-end conditions and an in
terruption signal to theCPU. A command can be rejected during execution of
STARTI/O, however, by a busy condition, program
check, etc. The rejection of the command is indicated
in the condition code in the psw, and the details of
the conditions that precluded initiation of theI/O op
eration are provided in the channel status word stored
when the command is rejected.
Channel Status Word
The channel status word (csw) provides information
about the termination of anI/O operation. It is formed
or reformed by STARTI/O, TEST I/O, or by an I/O in
terruption. Figure 21 shows the csw format.
Command Address
o 34 7 8 31
Status Count
32
47 4863 Bits 0-3 contains the storage-protection key used in the
operation.
Bit 4-7 contain zeros.
Bits 8-31 specify the location of the lastCCW used.
Bits 32-47 contain anI/O device-status byte and a channel
status byte. The status bytes provide such information as data
check, chaining check, control-unit end, etc.
Bits 48-63 contain the residual count of the lastCCW used.
Figure 21. ChannelStatus Word Format Input / Output Interruptions
Input/output interruptions are caused by termination
of anI/O operation or by operator intervention at the I/O device. Input/output interruptions enable the CPU to provide appropriate programmed response to
conditions that occur inI/O devices or channels.
Input/output interruptions have two priority se
quences, one for theI/O devices attached to a chan
nel, and another for channel interruptions. A channel
establishes interruption priority for its associatedI/O devices before initiating an I/O interruption signal to
the cpu. Conditions responsible forI/O interruption
requests are preserved in theI/O devices or channels
until they are accepted by theCPU. System Control Panel
The system control panel provides the switches, keys,
and lights necessary to operate and control the system.
The need for operator manipulation of manual con
trols is held to a minimum by the system design and
the governing supervisory program. The result is few
er and less serious operator errors.System Control Panel Functions
The main functions provided by the system control
panel are the ability to: reset the system; store and
display information in main storage, in registers, and
in the psw; and load initial program information.
System Reset
The system-reset function resets theCPU, the channels,
and online control units andI/O devices. In general,
the system is placed in such a state that processing
can be initiated without the occurrence of machine
checks, except those caused by subsequent machine
malfunction.Store and Display
The store-and-display function permits manual inter
vention in the progress of a program. The function
may be provided by a supervisory program in con
junction with properI/O equipment and the interrupt
key.Or, the system-control-panel facilities may be
used to place theCPU in the stopped state, and then
to store and display information in main storage, in
general and floating-point registers, and in instruction
address portion of the psw.
Initial Program Loading
The initial-program-Ioading(IPL) procedure is used
to begin or renew system operation. The load key is
pressed after an input device is selected with the load
unit switches. This causes a read operation at the
selected input device.Six words of information are System Structure 21
may be one or more bytes long. It provides detailed
information concerning the selected
as a stacker-full condition of a card reader or a fiIe
protected condition of a reel of magnetic tape on a
tape unit.
the
Transfer
The transfer-in-channel command specifies the loca
tion of the next ccw to be used by the channel when
ever the programmer desires to break the existing
chain of ccw's and cause the channel to begin fetch
ing a new chain of ccw's from a different area in
main storage.
External documents, such as punched cards or mag
netic tape, may carry ccw's that the channel can use
to govern reading of the external document being
read.
Input/output operations normally terminate with de
vice-end signal and channel-end conditions and an in
terruption signal to the
START
check, etc. The rejection of the command is indicated
in the condition code in the psw, and the details of
the conditions that precluded initiation of the
eration are provided in the channel status word stored
when the command is rejected.
Channel Status Word
The channel status word (csw) provides information
about the termination of an
or reformed by START
terruption. Figure 21 shows the csw format.
Command Address
o 34 7 8 31
Status Count
32
47 48
operation.
Bit 4-7 contain zeros.
Bits 8-31 specify the location of the last
Bits 32-47 contain an
status byte. The status bytes provide such information as data
check, chaining check, control-unit end, etc.
Bits 48-63 contain the residual count of the last
Figure 21. Channel
Input/output interruptions are caused by termination
of an
conditions that occur in
Input/output interruptions have two priority se
quences, one for the
nel, and another for channel interruptions. A channel
establishes interruption priority for its associated
the cpu. Conditions responsible for
requests are preserved in the
until they are accepted by the
The system control panel provides the switches, keys,
and lights necessary to operate and control the system.
The need for operator manipulation of manual con
trols is held to a minimum by the system design and
the governing supervisory program. The result is few
er and less serious operator errors.
The main functions provided by the system control
panel are the ability to: reset the system; store and
display information in main storage, in registers, and
in the psw; and load initial program information.
System Reset
The system-reset function resets the
and online control units and
the system is placed in such a state that processing
can be initiated without the occurrence of machine
checks, except those caused by subsequent machine
malfunction.
The store-and-display function permits manual inter
vention in the progress of a program. The function
may be provided by a supervisory program in con
junction with proper
key.
used to place the
to store and display information in main storage, in
general and floating-point registers, and in instruction
address portion of the psw.
Initial Program Loading
The initial-program-Ioading
to begin or renew system operation. The load key is
pressed after an input device is selected with the load
unit switches. This causes a read operation at the
selected input device.