IBM System/360 Operating Guide

conclusion of execution of the instruction in which
a match occurs. All pending interruptions are taken
before the clock stops.
ROS Control Switch
This switch is primarily for Field Engineering use.
ROS Scan Position
This mode is used when certain diagnostic tests
(scan ROS or read/write storage) are run.
Inhibit CF Stop Position
In this mode, processing occurs in the normal
fashion except that microprogram stops (determined
by the CF field) are ignored.
Process Position
This position is used for normal program processing.
PUSH BUTTONS
Several push button switches are provided to allow
the operator to perform manual operations or to
initiate system functions. The title given to each
button describes the resulting function when the
switch is operated.
Power-On Key,
Power-Off Key, and
Emergency Pull Switch
These controls are discussed in the Operator's
Control Panel section.
System Reset Key
Pressing this key resets the CPU clock, all regis-
ters (except the general-purpose and floating-point
registers in local storage), the controls in the CPU,
and all I/o units (including all sense and status for
the I/O units). In addition, when the Start key is
pressed after operation of the System Reset key,
the Basic Test and UCW Reset microprograms are
initiated. (The Basic Test routine is looped 128
times, so disregard the various error indicators
during this time.) See the ROAR Reset Key section.
Also, when the System Reset key is operated,
the current system mask is reset. However, upon
12
restart, the same current system mask controls the
system if that mask in local storage has not been
altered before restart (see Current Program Status
Word Selection section).
ROAR Reset Key
This key is used to manually alter the ROAR address
(WX registers) from the contents of switches F, G,
H, and J. The ROAR Reset key is active only when
the CPU clock is stopped; its function is initiated
when the Start key is pressed.
If the ROAR Reset key is pressed after a System
Reset function but before the Start Key is pressed,
the Basic Test and Clear UCW microprograms are
not initiated, that is, the UCW flag bytes in the MPX
storages are not reset to zeros.
Start Key
If the Start key is pressed after a normal stop (for
example, after the Stop key is pressed), instruction
processing continues as if no stop had occurred.
Machine status is unaffected.
If the Start key is pressed after a Start Reset
function, the Basic Test routine is performed, and
the Clear UCW routine resets all UC\V flag bytes to
zeros. If the Start key is operated again, the PSW
located at address 0000 is loaded into circuitry, and
processing starts. (See Start Reset Key and ROAR
Reset Key sections. )
Set IC Key
This key is used to manually alter the Instruction
Counter (IC) address from the contents of switches
F, G, H, and J, and is active only when the CPU
clock is stopped (Manual light is on). When the Set
IC key is pressed, the altered instruction address
is displayed in the B- and A-registers, and the
system stops. Any outstanding channel share cycles
are completed before this microprogram stop 0 ccurs.
Processing begins at the new instruction address
when the Start key is pressed.
If the Set IC key is pressed after a System Reset
function, the instruction counter is set to the address
entered from switches F, G, H, and J.
Check Reset Key
This key resets all machine-check logic circuits.
The Check Reset key may be used at any time (C PU
clock running or stopped).

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English