reset function, is honored when the CPU is again in
the operating state and enabled for the interruption.
A machine error that occurs in a manual operation
from whieh recovery cannot be made terminates the
operation, and the CPU is placed in the check-stop
state.
The following table lists operator controls that are
provided on all models. Some models provide addi­
tional controls.
Address-Compare Controls
These eontrols provide a means of setting a main­
storage address and stopping the CPU when the
address set up on the controls matches the address
used in a main-storage reference. One of the address-compare controls provides
two or more settings to specify the action to be tak­
en, if any, when the address match occurs. The two
settings are labeled "normal" and "stop." Placing
this control in other than the normal setting causes
the test indicator to go on.
The "normal" setting disables the address­
compare operation.
The "stop" setting causes the CPU to enter the
stopped state on a match. The point at which the CPU enters the stopped state depends on the model
and the type of reference. Pending I/O, external,
and machine-check interruptions mayor may not be
taken before the stopped state is entered.
In addition to the control for selecting the action
to be taken, another control may be provided for
specifying the type of main-storage reference which
is to be compared. A model may provide one or
more of the following settings, in addition to others:
The "any" setting causes the address comparison
to be performed on all main storage references.
The "data-store" setting causes address compari­
son to be performed when main storage is addressed
to store data.
The "I/O" setting causes address comparison to
be performed when main storage is addressed by a
channel to transfer data or fetch a channel command
word. Whether references to a channel address word !\lame Typical Implementation Address-Compare Controls Check-Stop Indicator Configuration Controls Display-and-Enter Controls Emergency··Pull Switch Enable·System-Clear Key IMPL ContliOls Interrupt Key*
Load I ndicator*
Load Key*
Load-Un it-Address Controls*
Manual I ndicator* Power-Off IKey* Power-On Key* Rate Control Restart KeV Start Key Stop Key Store-Status Key System I ndicator*
System-Res,et Key
Test I ndicator* Thermal/CB Power Check Indicator TOO Clock key*
Wait I ndicator* Explanatio,!: Rotary switches and toggle switch
2 One or more lights
1 110tary switches, toggle switches, and pushbuttons
Keyboard-printer
2
,3 Pull switch
Pushbutton
2
Pushbutton
2
,3
Pushbutton
2
Light
1
Pushbutton
2
Rotary switches
2
Light
1
Pushbutton
Pushbutton, backlighted
Rotary switch
2
Pushbutton
2
Pushbutton
2
Pushbutton
2 Special keyboard mnemonic
2
, 3
Light
1
Pushbutton
2
Light
1 One or more lights
Spring-return toggle switch
Light
1
* Remote operator control panel, if available, also contains this function.
1 Or the indicator may be on a CRT display.
2 Or the function may be provided by an equivalent keyboard input or a CRT-menu selection.
3 Or the function may be provided by pushbuttons, rotary switches, or both.
Operator Controls 244 Systl!m/370 Principles of Operation

or a channel status word cause a match to be indicat­ ed depends on the model.
The "IC" setting causes address comparison to be
performed when main storage is addressed to fetch
an instruction. The low-order bit of the address set­ ting mayor may not be ignored. The match is indi­ cated only when the first byte of the instruction is
fetched from the selected location. It is not indicated
for the instruction designated by EXECUTE.
Depending on the model and the type of refer­ ence, address comparison may be performed on logi­ cal, real, or absolute addresses, or controls may be
provided to specify the type of address.
The address-com pare-control settings can be
changed without disrupting CPU operations other
than causing the address-comparison stop.
Check-Stop Indicator
The check-stop indicator is on when the CPU is in
the check-stop state. The check-stop indicator may
be a separate indicator, or some models may use a
combination of other indicators to signal the check­ stop state. Performance of CPU reset turns off the
indicator. The manual indicator may also be on in
the check-stop state.
Configuration Controls
Configuration controls provide a means for setting
and controlling the configuration of the system. Some of these controls are associated specifically
with mUltiprocessing. The detailed function provided
depends on the model.
Display-and-Enter Controls
The system console provides controls and proce­ dures to permit the operator to display and enter
information in main storage, the general, floating­ point, and control registers, the PSW, and the keys
in storage. The CPU must first be placed in the
stopped state.
The display-and-enter functions are provided on
some models by means of controls on the operator
section of the system control panel; on other models,
they are provided by the use of the console device.
The CRT -menu-selection method may be provided
to facilitate the selection of storage facilities and
addresses.
Controls may be provided for data formatting,
checking, and error indication by means of interac­ tive procedures used on a keyboard-printer or a
keyboard-CRT device. In some models, enter-and­ display operations cause the manual indicator to be
turned off and may cause the start and restart keys
to b(! inoperative.
Main storage addresses for display-and-enter
operations are real addresses when dynamic address
translation is specified. Some models also include
the capability of specifying a logical or absolute ad­ dress.
Emergency-Pull Switch
Activating the emergency-pull switch turns off all
power beyond the power-entry terminal on every
unit that is part of the system or that can be
switched onto the system.
The switch latches in the out position and can be
restored to its in position only by maintenance per­ sonnel.
When the emergency-pull switch is in the out
position, the power-on key is ineffective.
Enable-System-Clear Key
Activating the enable-system-clear key, in conjunc­ tion with the load or system-reset key, results in the
performance of the system-clear-reset functions
described in detail in "Resets" in the chapter "System Control." In some models, the combination
of the enable-system-clear key with the load key or
the system-reset key is provided as an integrated
selectable function.
IMPL Controls
Controls are provided in some models for initial
microprogram loading (IMPL). These controls are
model-dependent.
Interrupt Key
Activating the interrupt key causes an external­ interruption condition to be generated.
The interruption is taken when the CPU is ena­ bled for the interruption and is in the operating
state. Otherwise, the interruption request remains
pending.
The interrupt key is effective while power is on
the system.
Load Indicator
The load indicator is on during initial program load­ ing; it goes on when the load key is activated and
goes out after the loading of the new PSW is com­ pleted successfully.
Load Key
Activating the load key causes a reset function to be
performed and initial program loading to be started.
Whether the enable-system-clear control is activated
at the same time determines the type of reset func- System Console 245