Code converter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Code converters are used to translate one form of a number into another. Their input and output variables are uniquely related to each other. This connection can be defined by switching tables or logic functions.

The encoder converts a single signal into an n-bit binary code. It finds the greatest application in information input devices (control panels) for converting decimal numbers to a binary number system. Suppose there are ten keys on the remote control with engraving from 0 to 9. When you press any of them, a single signal (XO-X9) is sent to the encoder input. The binary code (Y1, Y2,...) of this decimal number should appear at the output of the encoder. As you can see from the switching tables, in this case you need a converter with ten inputs and four outputs.

At the output Y1, the unit appears when any odd key X1, X5, X7 is pressed. X9. X1, i.e. Y1=X5\/X7\/X9\/X2\/X2. For other outputs, the logical expressions are: Y6=X7\/X4\/X4\/X5; Y6==X7\/X8\/X8\/X9; Y1=XXNUMX\/XXNUMX. Therefore, the encoder will need four OR elements: five-input, two four-input and two-input, fig. XNUMX.

Fig. 1

Decoder converts the code at its inputs into a signal at only one of its outputs. Decoders are widely used in control devices, in digital indication systems, for building pulse distributors for various circuits, etc. The decoder symbol on the K155ID1 chip with ten outputs for decoding one bit of the 8421 binary-coded decimal code and part of its circuit diagram are shown in Figure 2. Any input binary code corresponds to a low level on only one output, while all the others remain high. Decoders are included in all series of TTL and CMDP microcircuits. For example, the decoder K155ID4 (two decoders in the case) converts the binary code into the code "1 of 4", K155ID1 and K176ID1 into the code "1 out of 10", K155IDZ-V the code "1 out of 16". The pinout of these microcircuits is shown in fig. 2 and 3.

Fig. 2

The decoder on the K155ID1 chip is designed to work with ten-day gas-discharge indicators. Its outputs are connected directly to the cathodes (in the form of decimal digits) of a gas-discharge indicator, the anode of which is connected through a resistor to a power supply with a voltage of 200-250 V. The output signals of this microcircuit differ from TTL levels and therefore additional matching devices must be used to connect other microcircuits to it.

Fig. 3

The K155ID4 microcircuit consists of two decoders for 4 with combined address inputs (pins 3 and 13) and separate strobing inputs. Gating is the selection of a signal at a certain point in time. In this case, this is the appearance of the output signal at the moment when there are enabling levels at the gate inputs. If there are low levels at both inputs A1 and A2, then the output of the top decoder according to the scheme, the number of which corresponds to the equivalent of the input code, will be low. For the lower (according to the scheme) decoder, the following conditions are necessary: ​​A3==1 and A4==0. Figure 3b shows how this chip can be used as a decoder for eight outputs with a strobe input.

The decoder on the K155IDZ chip has four inputs for receiving numbers in the 8421 code and 16 outputs. Two strobing inputs (low levels must be applied to A1 and A2 to transmit a signal) allow you to combine microcircuits to obtain decoders for 32 outputs fig. 4, 64 outputs (four chips required), etc.

Fig. 4

BCD converter to seven-segment indicator code. The numbers on the scoreboard and consoles are displayed, as a rule, in decimal code. To do this, you can use a decoder on the K155ID1 chip together with a gas discharge indicator. However, the use of such indicators in amateur radio practice is undesirable due to the relatively high voltage of the power source (200 V). Now the so-called seven-segment LED and liquid crystal indicators, which operate at the same voltage as microcircuits, have become widespread. In them, the indication is carried out by seven elements, as shown in Figure 5. By applying a control voltage to the individual elements of the indicator and causing it to glow (LED indicators) or change its color (LCD indicators), you can get an image of the decimal digits 0, 1, ..., 9. I will talk about specific types of seven-segment indicators later. The conversion of the binary-coded decimal code to the seven-segment indicator code is shown in the table. The pinout of some microcircuits - converters of the 8421 code into a seven-segment one is shown in fig. 5.

Fig. 5

It is not the K514 series microcircuits that receive TTL input signals. The G signal is used to extinguish the low voltage indication. During normal operation, the signal level G=1. The decoder on the K514 chip works with LED indicators that have separate anodes, on the K514ID2 - with separate cathodes. The K514ID2 decoder is connected to the indicators through current-limiting resistors (200-500 Ohms), the first one has such resistors in its case.

Microcircuits K176ID2 and K176IDZ are code converters with an output memory register. The information is written to the memory at the edge of the clock signal applied to the input S (in this case, the signal at the input K=0). If K=1, the decoder is blocked. The output code of these decoders is direct at M=0 and reverse at M=1. The decoder is designed to work with liquid crystal and luminescent indicators. They can also work with LED indicators at a power supply voltage of 9 - 12V with a reduced brightness of the glow (due to current limitation to 2-3 mA).

Multiplexer a node that converts parallel digital codes into serial ones. It is used to sequentially interrogate a given number of information signals and transfer them to one output.

Fig. 6

The symbol of the multiplexer with four information inputs and its circuit diagram is shown in fig. 6. The logic level of that information input D is transmitted to the output Q of such a device._i, whose number id in binary code is set at the address inputs A1 A2. It follows from the schematic diagram that:

Q=D0(-A1)(-A2)\/D1A1(-A2)\/D2(-A1)A2\/D3A1A2.

The number of information inputs can be increased, but the word length of the address will also increase.

Author: -=GiG=-, gig@sibmail; Publication: cxem.net

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