Page 103 - Understanding Automotive Electronics

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3 ELECTRONICS FUNDAMENTALS

J-K Flip-Flop

The J-K flip-flop circuit A flip-flop where the uncertain state of simultaneous inputs on R and S is
is superior to the R-S solved is shown in Figure 3.9b. It is called a J-K flip-flop and can be obtained
flip-flop circuit because from an R-S flip-flop by adding additional logic gating, as shown in the logic
it resolves ambiguities diagram. When both J and K inputs are 1, the flip-flop changes to a state other
resulting from simulta- than the one it was in. The flip-flop shown in this case is a synchronized one.
neous inputs. That means it changes state at a particular time determined by a timing pulse,
called the clock, being applied to the circuit at the terminal marked by a
triangle. The little circle at the clock terminal means the circuit responds when
the clock goes from a high level to a low level. If the circle is not present, the
circuit responds when the clock goes from a low level to a high level.

Synchronous Counter
Figure 3.10 shows a four-stage synchronous counter. It is synchronous
because all stages are triggered at the same time by the same clock pulse. It has
4
four stages; therefore, it counts 2 or 16 clock pulses before it returns to a
starting state. The timed waveforms appearing at each Q output are also shown.
It is easy to see how such circuitry can be used for counting, for generating
other timing pulses, and for determining timed sequences. One can easily
visualize how such stages can be lined up to store the digits of a binary number.
If the storage is temporary, then such a combination of stages is called a register.
If storage is to be more permanent, it is called memory.
Digital counter circuits Digital clocks, as well as circuits that convert binary numbers to decimal
can easily be arranged to numbers so they can be displayed and read by humans, are made up of many
develop circuits that are stages of such counting circuits.
used in digital clocks. To review what has been discussed about digital circuits:
1. They operate with signals at discrete levels rather than with signals whose
level varies continuously.
2. High and low voltage levels are commonly used to represent the binary
numbers 1 and 0, respectively.
3. Combinations of ones and zeros can be used as codes to represent num-
bers, letters, symbols, conditions, and so forth.
4. Circuits called gates (Figures 3.6 and 3.7) can be combined to make logi-
cal decisions.
5. Circuits called flip-flops (Figure 3.9) can be used to store ones and
zeros. They can be set or reset into particular binary sequences to pro-
duce or store digital information, to count, or to produce timed digital
signals.
6. Transistors are used in the on and off condition in circuits to form gates
and flip-flops.

90 UNDERSTANDING AUTOMOTIVE ELECTRONICS