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Functional Characteristics of Manual Controls
Source: GA22-7000 IBM System/370 Principles of Operation
The manu a! controls provided on the
System/370
system console vary according to
model. This list defines the functions of
S/370
manual controls generally.
POWE R·ON pushbutton
Starts a power·on sequence. Lights up red, light turns
white after 30 seconds. Clear system reset occurs.
System enters manual stop condition.
POWER·OFF key
Initiates a power-off sequence when the power·on key
is lighted white or red.
START key
Starts instruction execution. Effective only if CPU is
in stopped state.
STOP key
Puts CPU in stopped state.
RESTART key
Initiates restart interruption. Effective in both operat·
ing and stopped states.
EMERGENCY PULL switch
Turns off all power beyond the power·entry tenninal
on every unit that is part of the system or can be
switched onto the system.
IMPL controls
Model dependent. Used for initial microprogram load·
ing.
LOAD key
Loads an IPL program.
LOAD indicator
Goes on when the LOAD key is pressed, goes off
when the IPL chain is broken.
LOAD UNIT-ADDRESS
Tells the system where to get the IPL program when
controls
you push the LOAD key.
TOD CLOCK key
Must be in ENABLE position to set ciock.
DISPLAY and ENTER
Control of these functions on some models is on the
controls
system control panel; on other models, by use of
console devices. CPU must first be placed in stopped
state. Using these controls, you can display and enter
information in main storage, in the general, floating-
point, and control registers, the PSW, and the keys in
storage.
ADDRESS COMPARE switch
Stops the CPU when it reaches any address you select
in advance. Settings can be changed without disrupting
CPU operations other than the stop.
INTERRUPT key
Interrupts program execution by causing an extemal
interruption. Interrupt is taken when CPU is in opera-
ting state, otherwi.e it remains pending.
SYSTEM RESET key
Interrupts instruction processing and resets the CPU,
channels, storage units and other CPU's.
ENABLE SYSTEM·CLEAR
In conjunction with SYSTEM RESET key, resets the
key
CPU, channels, - on-line nonshared control units, and
1/0 devices; and, in most models, ciears registers to
zeros. In conjunction with LOAD kay, does the same
except you must re-I PL.
RATE CONTROL
Sets the rate the CPU will operate at: PROCESS rate,
normal speed; INSTRUCTION STEP rate, one whole
instruction per push of the START key. Set when
CPU is in stopped state. TEST indicator lights when
RATE CONTROL is not set to PROCESS.
Page 3-1
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