Figure 4-12.—Example of a synchronous operation with a
flip-flop.
T (Toggle) flip-flop —Changes state on
command from a common input terminal
D (Data) flip-flop (latch) —Uses a data input and
clock input
J-K flip-flop —May perform the function of an
R-S, T, or D flip-flop (the most versatile)
FLIP-FLOP OPERATIONS. —Some of the
operations associated with flip-flops are as follows:
Synchronous operations —This term describes
the operation of logic functions that are controlled by
the occurrence of a specific timing signal. Usually the
timing signal is the computer’s timing signal and is
commonly referred to as the clock pulse. See figure
4-12.
Asynchronous operations —This term describes
the operation of logic functions that are not controlled
by the occurrence of a specific timing pulse. Refer to
figure 4-13.
Figure 4-13.—Example of an asynchronous operation with a
flip-flop.
Gated (latched) operations —This term is used
when describing logic functions that can be turned on
or turned off, dependent upon an input control signal
(command or enable). See figure 4-14.
FUNCTIONAL USES OF
DIGITAL IC’S
We can divide the functional uses of digital ICs into
two distinct areas. There are those IC circuits that make
decisions based on their inputs, and there are IC circuits
that hold the data in memory-type circuits. They are
used together to route the data throughout the computer.
Let’s begin with the decision-making functions.
Decision-Making Functions
Decision-making functions consist mainly of
combinational gates. For every combination of bits in
the various input wires, there is a definite, prearranged
combination in the output wires to be decided upon.
The output combination is the same every time a
particular input combination occurs. Gates are grouped
together in various combinations to form the
decision-making circuits. Decision-making functions
in the computer can be separated into two distinct
classes—code converter circuits and data routing
circuits.
CODE CONVERTER CIRCUITS. —Code
converter circuits are capable of encoding data to a
usable form for the computer and decoding the data so
it can be displayed or used by a peripheral. An example
of encoding and decoding on a microcomputer is given
Figure 4-14.—Example of a gated operation.
4-11
