MAN/MACHINE OPERATING MODES
Controlling the tempo of instructions through
man/machine interfaces can be executed in several
modes of operation.
The two most commonly
encountered operating modes are run and stop. Other
modes are step, sequence, and phase.
When the computer is in run mode, it continually
executes instructions one after another as directed by its
logic circuits and software. The speed of execution is
determined by the timing circuits or clock of the CPU.
When the computer is stopped, it is not executing
an instruction and will not execute an instruction until
directed by an operator action (START or RUN
pushbutton with the instruction address in the program
counter). A running computer can be stopped by
manual action (STOP pushbutton) or by execution of a
STOP instruction under program control. Many
microcomputers and embedded microprocessors do not
have or do not use their STOP mode except from the
device maintenance panel. During normal operation,
they are designed to run continually from firmware
programs once the equipment they are in is powered up.
The only way to stop a microcomputer is to power it
Most computers or microprocessor controlled
peripherals with maintenance panels offer the
technician other modes of operations, specifically some
form of instruction step. In the instruction step mode,
individual instructions are executed one at a time as
directed by the technician (pushbutton or toggle switch
action) or in some machines at a slower than normal rate
as determined by a manually adjustable low-speed
oscillator. The contents of the computer registers and
memory locations can be tested by the technician at the
end of each instruction to verify proper operation or to
aid in troubleshooting the computer. In newer
computers, instruction step may be divided into two
levels: macro step or micro step.
MACRO STEP. A macro step allows the
execution of a single microinstruction. Those
computers using macroinstructions composed of a
series of micro instructions may give you the option to
instruction step at either level, macro by macro or micro
by micro within an individual microinstruction.
MICRO STEP. A micro step allows the
execution of a single microinstruction.
Sequence mode allows the execution of one
sequence of an instruction at a time. Each operation of
an instruction has an established set of sequences to
complete the instruction. This enables you to execute
one sequence of an instruction at a time. This is useful
for detailed troubleshooting of an instruction.
Phase mode allows the execution of one phase of
an instruction at a time. If a computer has six main
timing phases, you can execute one phase at a time. You
can see what the instruction has accomplished at the end
of each phase.
This is also an aid for detailed
Interface capabilities available vary from computer
M i c r o s r e l y o n k e y b o a r d s a n d m o u s e
devices to interface; consult your computers manuals
for detailed operations. Because more hardware is used
on mini and mainframe computers, their interface
capabilities provide a greater range to set parameters
and control the operations of the computer more closely.
This is particularly useful in the preventive and
corrective maintenance aspects of your job. Without
going into detail, the following functions are commonly
available to the technician through the man/machine
interface operating modes. Some are self-explanatory;
we describe their basic operations.
Master Clear Clears all I/O and CPU registers
and will stop the computer if it is in the run mode
Start/Run Starts the function determined by
the operating mode(s)
Stop (computer control) Causes computer
operations to stop
Stop (program control) causes corresponding
stops to occur under program control
Jump Causes corresponding jump to occur
under program control
Bootstrap Addresses NDRO (ROM)
depending on position of AUTO RECovery or