IBM System 360 Operating Manual page 13

Stop Key
When this key is pressed, the system enters the
stopped state when:
1. The instruction being processed has been com-
pleted,
2. All pending interruptions have been serviced,
and
3. Any I/O operation in progress has been finished.
If data or command chaining is involved, it is
completed before the CPU clock is stopped. The
System light stays on as long as any I/O unit (except
the 1050) is engaged in an I/O operation; that is
until device-end is accepted for the last command
in a chain for that I/O device).
Note that the machine environment is not de-
stroyed and the program that was in progress can be
restarted (by operation of the Start key). The
address of the next instruction is displayed in the
B- and A-registers.
When the system is in the stopped state, the
multiplexor channel is allowed to accept share-
request traps (microprogram branches), and the
selector channel is allowed to accept data cycles.
This provision permits input-terminal and multi-
system operations even though the 2030 program in
progress has been manually interrupted.
Even though these operations are in progress,
data can be stored or displayed. At the instant a
cycle is being used for a channel operation, the
manual store and display circuits are inactive.
However, if the Store or Dis play key is held
operated, the data is stored or displayed. If the
store key is operated only during a channel-operation
cycle, the data to be manually stored is not stored.
It is advisable, therefore, to display any location
(in which data is manually stored) so that storing
can be verified.
Interval Timer Switch (INT TMR)
When the Interval Timer feature is installed and
this switch is on, the interval timer is allowed
to generate program interruptions. If the switch
is off, the interval timer is ignored and the main-
storage timer locations are not changed.
Store Key
This key causes the hexadecimal byte specified
by switches Hand J to be entered into the area
selected by the Display Storage Selection dial (switch
E).
If a register is selected by switch E, the data
byte is entered into that register and displayed in
both the B- and A-registers. Information cannot be
stored in all the registers selectable by switch E.
See the Store and Display Section.
When main storage (MS) or auxiliary storage
(AS) is selected by switch E, switches A, B, C, and
D specify the address into which the data byte is
stored. The data byte (from switches Hand J) is
displayed in both the B- and A-registers.
The CPU clock must be stopped for the store
operation. If main or auxiliary storage is being
accessed, the Allow Write light must be off.
Lamp Test Key
Pressing this key causes all indicator lights on the
2030 console to turn on. This test does not affect
system operation and can be performed during
program execution if desired. (The console lamps
will be slightly dimmer than during normal operation. )
Display Key
The function of this key is similar to that of the
Store key, except that the accessed location. is not
altered. The Display key is provided so that regis-
ters that do not have their own console indicators
can be displayed.
Main-storage (MS) and auxiliary-storage (AS)
locations are displayed by setting switch E to the
storage area deSired, and switches A, B, C, and
D to the address of the location to be displayed.
The Main Storage Data Register (MSDR) is used to
display the contents of the accessed storage location.
If the original value in the MSDR will be needed
when the program is restarted, record this value so
the MSDR can be restored after the display operation.
If the ROS control, Rate, Address Compare, and
Check Control switches are all set to Process, and
the system is allowed to come to a normal stop
(Stop key was pressed and the manual light is on),
the contents of the M SDR need not be restored before
the Start key is pressed to resume program operation.
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