Page 259 - Mechanical Engineers' Handbook (Volume 2)
P. 259
248 Digital Integrated Circuits: A Practical Application
A A
OR f NOR f
B B
f = A + B f = A + B
A B f A B f
0 0 0 0 0 1
0 1 1 0 1 1
1 0 1 1 0 1
1 1 1 1 1 0
Figure 10 Gate logic symbol for OR and NOR gates with their respective truth table.
of indicating 0000 to 1111 (base 2). The term modulo is used to describe the count capability
of counters; that is, modulo-16 for a four-stage binary counter, modulo-11 for a decade
counter, modulo-8 for a three-stage binary counter, and so on. Ripple counters, as shown in
Fig. 11, are so named because the count is like a chain reaction that ripples through the
counter because of the time involved. The ripple counter is also called an asynchronous
counter. Asynchronous means that the events (setting and resetting of FFs) occur one after
the other rather than all at once. Because the ripple count is asynchronous, it can produce
erroneous indications when the clock speed is high. A high-speed clock can cause the lower
H
Q J Q J Q J Q J
Clk Clk Clk Clk
K K K K
FF4 FF3 FF2 FF1
D C B A
Q
Q
Q
Q
Figure 11 Logic and timing diagram of a four-stage ripple counter.
