Page 143 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

124 H Chapter Eleven

j s. 01

>
clock
clock > 3-q
k 3-q
i I I

Figure 11-18, JK and T flip-flops

T flip-flop doesn’t have any data inputs; the outputs simply toggle to the
inverse of their previous values on each active edge of the clock input.

Shift Registers

As was previously noted, another term for a flip-flop is “register.” Functions
known as shift registers-which facilitate the shifting of binary data one bit at a
time-are commonly used in digital systems. Consider a simple 4-bit shift
register constructed using D-type flip-flops (Figure 1 1 - 19).
This particular example is based on positive-edge triggered D-type flip-flops
with active-low -clear inputs (in this case we’re only using each register’s q
output). Also, this example is classed as a serial-in-parallel-out (SIPO) shift
register, because data is loaded in serially (one after the other) and read out in
parallel (side by side).
When the -clear input is set to I (its inactive state), a positive-edge on the
clock input loads the value on the serial-in input into the first flip-flop, dff[O].
At the same time, the value that used to be in dff[O] is loaded into dff[I], the