Binary encoder
It is sometimes necessary to binary encode the selection of one
signal from a
collection of them. This device effectively does the reverse
of a decoder. The diagram has been kept simple by showing
only two bits. It
should be fairly obvious
Arithmetic logic units
Half-adder
It is easily seen that 1-bit binary addition is equivalent to a XOR
operation and that the carry may be generated by an AND. The system
which performs a 1-bit binary addition with carry output is called a
half-adder .
A h
Accumulator machine
Programming constructs
The most basic construct, the sequence, is implemented using a counter called
the program counter (PC). It contains the address of the next instruction to be
fetched from memory and then executed. It is increment
Bi-directional shift register
We now progress to consider registers which are capable of operating on
the
data they contain.
The bidirectional shift register is capable of shifting its data right or left
by
one bit each clock tick. Each flip-flop input is
Boolean algebra
Boolean variables are variables with range cfw_1,0. It is hoped that the
reader has
already met and used them as a data type of a programming language.
Boolean algebra is designed to appear much like ordinary algebra in
order to make it ea
Bitwise logical operations
Most computations deal with numbers and symbols which require word
widths
greater than one. The memory of a computer is arranged accordingly.
There are,
however, still many occasions when this is inefficient, inconvenient or
dow
Boolean algebra
Specification
The behaviour of a purely combinational system must be determined by
the specification of a function. If the system input and output channels
are of binary digital form then we may regard each as a set of Boolean
variables. E
AND/OR STRUCTURES
Because every truth function may be realized as either the standard
product of
sums or the standard sum of products it is not uncommon to find
structures of the
form depicted. They are called two-level structures. The first level
produce
1-bit memory
It is very important to realize that any bistable system may be used to
implement a 1-bit memory.
The state adopted when energy is supplied will depend on which gate
(switch)
wins the race. However, the system may be disturbed into one or oth
Binary decoder
The first sub-component of interest is a system which decodes
a binary value. By
decoding is meant the assertion of a unique signal for each
possible value
input. Hence a 2-bit decoder has an input consisting of two
signals, one for each
bi