IBM System/360 Operating Guide

3. To store data, set the appropriate hexadecimal
representation of the information to be stored
into switches H and J. Press the Store key.
Figure 8 indicates the general functions of the
various areas that can be selected and where they
are displayed during display operation. It is im-
portant to realize that data overruns can occur
during single-cycle operations. Therefore, data
sent to or from an I/O device can be lost and the
resulting console indications may not be exactly
what is expected.
PROCESSING A PROGRAM SECTION
To examine the results caused by processing a
section of a program, use the following procedure:
1. Set the desired stop address in switches A, B,
C, and D and place the Address-Compare switch
(see Figure 2) in the SAR delayed stop position.
2. Load the program as described in the Program-
Load Routine section.
3. If the load program clears storage, press the
Start key after the first stop. Press the Start
key again after the second stop (this stop occurs
when the program is being loaded). The third
stop then occurs after execution of the instruction
(including all pending interruptions) in which the
address match occurred. You can now examine
conditions produced by the processing of the
program segment. Subsequent instructions can
then be processed, one at a time, by using the
procedure described in the Single-Instruction
Processing section.
The program may use the Interval Timer feature.
If so, the Interval Timer may decrement through
zero after tbe system has processed a program
segment and then entered the stopped state. Then,
when you restart the program, an interval timer
interruption will occur and you may not obtain the
desired results. If your program depends upon
the Interval Timer but you do not want to have
interval timer interrupts while checking out a
program segment, set the Interval Timer switch
to the OFF position (see Figure 2, lower left).
STARTING AT A SPECIFIC INSTRUCTION (SET IC)
PROCEDURE
1. Press the Stop key.
2. Set the desired instruction address in switches
F, G, H, and J.
3. Press the Set- IC key.
4. Press the Start key.
Note: If an invalid address is entered, a machine-
~ error will occur. The Check Reset key can
be used to clear this check condition.
Program processing starts at the instruction
address that was set into switches F, G, H, and
J. If you desire to stop just after a particular
instruction has been processed, use the procedure
described in the Process a Section of a Program
section.
An important point to note is that your program
segment may start in problem mode and stop in
supervisor mode. If you then attempt to start at
an instruction (by using the set-IC routine) that
should be handled in problem mode, the system
"sees" the problem instructions as if they were in
supervisor mode. (A program interruption occurs
if a privileged instruction is encountered in the
problem state.) The program run may then give
different results than expected. Therefore, you
should know, from your program, what mode you
are in when starting and stopping the program seg-
ment. If you are not sure, you can display local
storage location address B9 (hexadecimal). Bit 7
of
this location is the problem/supervisor bit of
the current PSW. When this bit is a zero, the CPU
is in the supervisor mode; when it is a one, the
CPU is in the problem mode.
If you are not in the desired mode, you can
manually alter bit 7 of local storage location B9.
Anyone performing this type of operation, however,
should have an intimate knowledge of the program
being used.
Other fields in the current PSW may have to be
altered due to the requirements of your program
segment. To avoid performing a number of manual
store operations, you can use the following proced-
ure:
1. Store a PSW in main-storage address O. (Any-
one performing this type of operation should
have an intimate knowledge of the program being
used because certain IBM programming systems
use main-storage addresses 0, 1, 2, etc for
other purposes.) This PSW is loaded with
information that applies to your program seg-
ment. For example, the mode (problem or
supervisor) system mask, and instruction
25

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English