IBM System/360 Operating Guide

I/O interruption conditions are reset when the
Power-Off Key is operated. Therefore, any pending
I/O interruptions are lost during a power-off opera-
tion.
The Power-Off key takes precedence over the
Power-On key.
The recommended power-off procedure is:
1. Press the console Stop key and wait for the
Manual light to come on. (The Stop keys on the
attached I/O units do not cause the system to
enter the manual state. )
2. Press the Power-Off key.
Emergency Pull Switch
The Emergency Pull Switch removes all primary
electrical power (including power to all on-line I/O
units) with no regard to sequencing. The contents
of storage may be altered if this switch is operated.
As the name implies, the Emergency Pull Switch
should be used only if necessary. This switch must
be manually reset by the Customer Engineer.
The system is protected by thermal overload
switches. If the temperature of the operating
environment is too high, these switches drop system
power. Contact the Customer Engineer whenever
system power cannot be maintained.
System (SYS) Indicator
This indicator is normally on whenever either of
the use meters is running. (See the Use Meters
section. )
Manual (MAN) Indicator
This light indicates that the CPU clock is stopped
and that no channel operation is in progress (as long
as the System light is off). Several of the manual
console controls are effective only when this lamp
is on.
\Vait Indicator
When this light is on, the CPU clock is running but
no instruction processing occurs. If an interruption
occurs, processing is initiated as required by the
program.
8
Test Indicator
The Test light is on whenever the Address Compare,
Check Control, ROS Control, or Rate switch is not
set to Process (normal processing position).
Load Indicator
This indicator turns on when the Load key is pressed
and released. It remains on until the load micro-
program is successfully completed (the initial-load
PSW is set into circuitry). See the Load Key section.
Load Key
This key is used to initialize the system. The f01-
10\ving functions occur:
1. An automatic System Reset is performed.
2. The CPU clock is started.
3. The basic test microprogram is performed.
This test is looped 128 times.
4. The clear UCW microprogram is run to reset
all the flag bytes in the UCW area of auxiliary
storage.
5. The load microprogram is begun. This routine
analyzes switches G, H, and J to determine the
address of the program-loading I/O device
(load-unit address). \Vhen this routine is com-
pleted, the Initial Program Load (IPL) PSW has
been successfully set up, and the Load light is
turned off.
Note that the system mask is reset when the load
key is pressed. The system mask in the IPL PSW
is then effective as soon as the IPL PSW is set up.
Interrupt Key
When this key is pressed, the interruption code of
the external old PSW is altered to indicate that an
external interruption is pending. The system recog-
nizes this interruption only if programmed to do so.
Switches F, G, H, and J
These rotary switches are normally used by the
operator for the following operations:

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English