SU1234973A1 - Device for decoding manchester code - Google Patents

Abstract

The invention can be used in automation and computing when creating digital data transmission systems. The invention allows to improve the noise immunity of the device. The device contains a receiver 1, a multi-branch delay line 2, a trigger 7, and a block 8, 12, and an interruptor consisting of a correlator 3, an upper threshold comparator 4, a lower threshold comparator 5, and an extremum detection unit 6. In the correlator 3, the convolution of a segment of the input code of Manchester with the reference combination chosen in accordance with the structure of this code is carried out. When the signal from the output of the correlator 3 crosses the corresponding threshold and the signal from block 6, corresponding to a change in the sign of the correlation function, occurs, the logical level changes at the output of trigger 7, i.e. decoding. The introduction of the correlator 3, comparators 4 and 5, and block 6 ensures correct decoding if there is a crushing or dominating type of interference in the input signal. 3 ill., 1 tab. with about (/). one

Description

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The invention relates to automation and computing and can be used in data transmission systems.

 The purpose of the invention is povpene better resistance.

FIG. 1 is a block diagram of a device for decoding a Manchester code; FIG. 2 shows an example of the execution of a block defined by the shadow of extrema; in fig. 3 - times: first diagrams of device operation.

To the input of the device for decoding the Shnchester code are connected a receiver 1 connected in series and a lot of & a delay line 2, the outputs of which are connected to the corresponding inputs of the correlator 3. The outputs of the correlator 3 are connected to the corresponding threshold inputs of the comparator 4 of the upper threshold, the comparator 5 of the lower threshold and block 6 for determining extrema, the outputs of which are connected respectively with the first and second informational and synchronous signals. trigger inputs 7. Correlator 3, comparators 4 and 5 and block 6 form a decision block 8.

The extremum determination unit 6 can be implemented using a register 9, a digital comparator 10 and a pulse shaper 11 (FIG. 2).

The device works as follows.

The input signal 5 in which the transmitted information (Fig. 3o) is encoded in the form of a Manchester code, (Fig. 3o) 5 comes from the communication line. to receiver 1, where it is amplified and converted into a pulse signal with the levels used in the device is logical (TTL, CMOS, etc.). From the output of receiver 1, the signal (FIG. 3 S) is fed to the information input of multi-drop line 2 overhead, as which, for example, you can use a serial shift register.

The signal found by w; and | 1c in line 2 of the delay at a fixed point in time can be interpreted as a binary combination S (S, S,. O, 8,), where S | is the value of the i-ro bit of the combination, am is the number of bits in the combination (m coincides with the number of taps of the delay line 2). This combination enters the correlator 3, which counts the number of matches by 234973 times,. - "

A series of combinations of S (S, S,.., S) with a combination of G (g,, g, ..., g, J, given the outcome of the Manchester code structure, and, converts this number of matches into a binary code.

Thus, the correlation function at the output of the correlator 3 is represented in the diffracted form. Analog equivalent of it is presented in figure 4. 10 The combination G (g, g, ..., g) is constant for a particular implementation of the correlator 3 and is permanently written in it. Practically, this means that the correlator 3 is built with regard to G (g, g, 15 gfr.) For example, when implementing a correlator 3 on a ROM, it is programmed in accordance with G (g, g ,.,., G).

Digital comparators 4 and 3 compare the value of the correlation function with the upper and lower thresholds. If the value of the correl and the ion function is 1; and more than the value of the upper threshold, a control signal 25 is generated at the output of comparator 4 (Fig. 4); if it is less than the value of the lower threshold, then a signal is generated at the output of comparator 5 (Fig. 4e).

The extremum determination block b 30 generates short pulses at time points corresponding to the inflection points of the correlation function (fig. 4e). These pulses are formed with the help of shaper 11 (fig. 2) at the moments of changing the sign of the derivative of the correlation function. These moments are determined using a digital comparator 10 comparing the current value of K, correlation of 35

40

function with the value K. in the previous step of the calculation from the outputs of the pfallell register 9. Comparator 10 operates in accordance with the following truth table:

45

50

K. K

K, K ,.

) ABOUT

55

K.K.

Controlled by the signals from comparators 4 and 5 are sent to the information

function with the value K. in the previous step of the calculation from the outputs of the pfallell register 9. Comparator 10 operates in accordance with the following truth table:

50

K. K

K, K ,.

) ABOUT

55

K.K.

The control signal from the comparators 4 and 5 is sent to information 31

The trigger inputs 7, which can change their state only by the signal of the estremum detection unit 6, are fed to the trigger input 7. If the control signal is present at the output of the comparator 4, the trigger 7 switches to zero cocTOHirae, and if the control signal is present at the output of the comparator 5, then the trigger 7 is switched to the single state. If the control signal does not have any comparator 4 and 5 output, then the trigger 7 does not change its state. The signal at the output of the trigger 7 is the result of the dc (Fig. 3c). This signal is identical to the transmitted message (Fig. For).

The effect of interference on the communication line causes Crushing-type distortion in the signal at the output of receiver 1. or predominance. Physically, this can be represented as the appearance of spurious values in the bits of the combination S (S jS,; -S) One possible type of distortion and its effect on the decoding result is shown in FIG. 3 dotted line. Distortions in the signal affect the correlation function, in which the side lobes and the maximum value are mixed (Fig. 46). However, it can be seen that for specific distortions these changes do not lead to false-correlation function through the upper and lower thresholds and, therefore, decoding is performed without distortion.

In the Manchester code, there are only two types of references: length - T duration and short duration T / 2. A parcel length means a change in the state of the original information code; in this case, if the value of the unit is one, then it means a transition from one state to zero, and if the value of the parcel is zero, then the transition from zero state B is unit.

From this it is possible to set the combination G (g, g ,,., Ge) for the correl

If you take that delay

Torah

signals between the co wednesdays

delay line 2 is equal to fit, it is long

T

the parcel is broken at disl

specific intervals. In this case

73, -

Combined G (g, g,..., g) can be specified as G (,..., 1 11, P. In this case.

It is obvious that with the full coincidence of the combinations S (S, S, ..., S) and G (g,

g,. . . , 0) correlation function

I.

has the value m, and with a complete mismatch, the value is 0. Such a specification of the combination G (g, g, ..., g) is not the only one; m. Directly from the structure of the Manchester code, it can be seen that the combination G (g, g, ..., g can be set not only on the interval T, but also on the interval up to 2T (taking into account p for example, that before and after a long dressing with a level of about There must be at least short dressings with a level of zero. In this case, the combination G (gf, §2, ..., g,) can be specified as G (g, g, ..., gj 00 ... 001 11 1.1100 ... 00. With this.

To set G (g, g, ..., g), you can use any intermediate combination of the two, which can be considered as boundary. With the correlation function, side lobes appear, however, the steepness increases.

The value of At is chosen from the compromise conditions. With large at, decoding accuracy is reduced and the effect of interference-free protection is reduced, while with small At, circuit costs increase.

It can be shown starting from the values of the side lobes of the correlation function that the selection of the values of the upper (VP) to the lower (LF) threshold can be made on the reflex of the expressions

VP 5 ha

When performing equality gets maximum noise immunity.

P

can be admittedly up to r

false values in combination S (S

s ,,.,., - sj.

FIG. 36 shows the analog equivalent of the correlation function at

provided.

Claims (1)

Invention Formula A device for decoding a Manchester code, containing a serially connected receiver and a line beyond the optimal limit. is at holders, a decisive block and a trigger whose output is the output of the device, and for example, in order to increase noise immunity, the decisive block consists of upper and lower threshold comparators, an extremum definition block and a correlator whose inputs are connected to the corresponding thresholds of the delay line, the outputs are connected to the corresponding inputs of the comparators of the upper and lower thresholds and the extremum determination unit, the outputs of which are connected respectively to the first and second informational and synchronizing inputs s trigger. fie.g but / t 7 I / I 1 g de f