Initial information about combinational devices, Methods of...

Initial information about combinational devices

Ways of presenting and describing combinational devices

Consider them.

Graphical method

The combination device can be represented as a multi-terminal (Figure 3.2), with M inputs, which are fed signals X m (m = 0, ..., M - 1), and N outputs from which the signals Y n (n = 0, ..., IV-1). This type of representation is called graphic or schematic. It is used to compile logic circuits of digital devices.

Analytical method

The peculiarity of both input X m and output Y n signals is that they can take only two values ​​- 0 and 1. Since in combinational devices signals Y n are uniquely determined by the combination (combination) of signals {X m }, acting on a certain time interval T,

Ways of processing and inputting/outputting code words: serial input and output (a), parallel input and output (b), serial input - parallel output (c) , parallel input - serial output (g)

Fig. 3.1. Ways of processing and inputting/outputting code words: sequential input and output (a), parallel input and output (b), serial input - parallel output (in), parallel input - serial output ( > g )

then in the general case the relationship between them can be specified in the form of a system of logical functions

(3.1)

Graphical representation of a combinational device

Fig. 3.2. Graphical representation of a combination device

The system (3.1) is an analytical description of combinational devices.

Tabular method

One of the most common ways of describing combinational devices is truth tables. The truth table contains:

• One column for storing numbers k or combinations of sets of input signals (decimal number, starting with zero);

M , which is usually identified columns for recording values ​​of the input signals with binary numbers and arranged in rows of the table in ascending order. Combinations of 0 and 1 make it possible to obtain K = 2 m different values ​​of numbers. For example, for M = 2 binary numbers take on the following values: 00, 01, 10, 11. Each k-u set (combination) of the input signals corresponds, according to (3.1) determined output value and on th Raman device output;

N columns for recording the values ​​of the output signals

The structure of the truth table for M = 2 is given below as an example (Table 3.2). The truth table provides exhaustive information about the functionality of the combination device and is widely used to describe them.

Table 3.2

k

Input signals

Output signals

0

0

0

0

0

0

0

0

0

0

0

1

1

1

1

1

1

1

1

1

0

1

0

0

0

0

1

1

1

1

0

0

0

0

1

1

1

1

2

1

0

0

0

1

1

0

0

1

1

0

0

1

1

0

0

1

1

3

1

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

thematic pictures

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