index (DCI) with error stop and recommended
corrective measures:
Replace pcbs in locations
4C28-4C30.
PATCH OR REVISE SOFTWARE. —
Mainframes also have the option to allow you to
manually insert and make revisions of machine code or
insert revisions using external peripheral devices.
Patches or revisions to the software are written by
authorized personnel only. The patches or revisions are
entered using inspect and change routines or
equivalents using the controls, data entry, and data
display man/machine interface.
SUMMARY—COMPUTER
INSTRUCTIONS AND MAN/MACHINE
INTERFACES
In this chapter we introduced you to computer
instructions and to ways you can interface with a
computer. The following information summarizes
important points you should have learned:
COMPUTER INSTRUCTIONS —Computer
instructions are commands to the computer to tell the
equipment to perform a designated operation. The
instructions are processed by the central processing
unit.
PROGRAMS. —Programs are sequences of
instructions written for various purposes to solve
problems or types of problems on a computer, to
manage the computer’s own resources and operations,
and/or to maintain computers.
LEVELS OF INSTRUCTIONS. —Instructions
may be either microinstruction or macroinstructions (a
predetermined set of microinstruction).
INSTRUCTION TYPES. —Instructions may be
classified by what they do, their operation. They may
also be classified by their action on an operand-read,
store, or replace.
INSTRUCTION SIZES. —Instruction sizes vary
depending on the instruction and the computer.
INSTRUCTION FORMATS. —Every instruc-
tion has an operation (op) code to tell the computer what
to do. It may also have an operand to give the address
of the data to be operated on or to give other fields or
designators.
INTERFACING WITH COMPUTERS. —The
man/machine interfaces enable operators/technicians to
control the computer’s operation. These include
control panels and operator panels/consoles.
MAN/MACHINE OPERATING MODES. —
Computers can be operated in a variety of modes. This
is very helpful when you are troubleshooting. Run
mode continually executes instructions one after
another. Stop mode causes the computer to stop; it will
not restart until directed by some operator action. Step
mode enables you to have the computer execute one
instruction at a time so you can test the contents of
computer registers and memory locations to verify
correct operation or identify a problem.
MAN/MACHINE INTERFACE OPERA-
TIONS. —Many operations can be accomplished by
providing information to the computer through an
interface.
MAN/MACHINE INTERFACE FUNC-
TIONS. —Many general functions can be performed
through an interface.
It is up to you to learn all you can about how the
computer systems you work with process instructions
and what capabilities are available to you through
man/machine interfaces. This will enable you to
interpret computer instructions and interface with the
computer to diagnose and isolate problems.
8-26
