Manchester Encoding - Basic Principles of Encoding
Lab Objectives
The practical study of the availability of the support of the basic principles of encoding in
Manchester encoding in the process of transformation of binary data into the Manchester
encoding and its transmission, namely:



The availability of fronts (positive or negative transitions at the center of each
transformed bit) in the Manchester encoding ensuring the possibility of synchronization
between the transmitter and the receiver.
Availability of additional steps in Manchester which ensures the possibility to minimize
the bandwidth of the signal spectrum.
Availability of differential character of the Manchester signal which ensures stability
regarding noises (external noise impact).
Lab Assignment
In the given work using the NETWORK TEST BENCH (NTB) board one shall carry out the
practical study of the availability of the support of the basic principles of encoding in
Manchester encoding in the process of transformation of binary data into the signals of
Manchester code and its transmission, namely:
 Availability of fronts in Manchester code ensuring the possibility of the synchronization
between the transmitter and receiver.
 Availability of additional steps in Manchester code ensuring the possibility of the
minimization of the signal bandwidth.
 Availability of the differential character of the Manchester encoding ensuring stability
regarding noises (external noise impact).
Requisite Equipment




A personal computer (PC) with installed operational system Windows 7 and installed
software package of National Instruments and a laboratory bench.
Workstation NI ELVIS II
NETWORK TEST BENCH board (NTB)
Mounted direct UTP network cable of category 5 with RJ-45 connectors (1 item).
Preparations

Install the NETWORK TEST BENCH board onto the NI ELVIS II workstation

Using direct network UTP cable connect RJ-45 connectors 1 and 2 of the transmitter and
receiver on NTB board
Switch on the NI ELVIS II workstation

Step-By-Step Instructions
1. Set the PROTOTYPING BOARD POWER switch (1) in (see Error! Reference source not
found. on p. Error! Bookmark not defined.) into the ON position, the green LED
PROTOTYPING BOARD POWER (2) and red LED in the lower left corner of the board
should turn ON.
2. In the Lab Software main menu double click to select the Manchester Encoding: Basic
Principles of Encoding lab. Click the Open button. The Lab software window will open
(Error! Reference source not found.).
3.
4.
5.
6.
Fig.Error! No text of specified style in document.-1 Lab software window
On the left side of the Lab software window the software equivalents of the binary
information physical switches (13) (Error! Reference source not found.) are located. The
MODE switch and SET/STOP button in the lab software are the software
representations of its physical ones: MODE (14) and SET/STOP (15) (Error! Reference
source not found.) of NTB board. Thus, the installation of these switches can be
performed as on the board directly, as well as through the Lab software. For switching
over between these two modes, use the switch MANUAL/PROGRAM MODE in Lab
software. In MANUAL MODE the switches and the button on the board are active, and
in PROGRAM MODE in Lab software.
Set the MODE switch (14) (Error! Reference source not found.) into the RECORD MODE
position.
Using the binary switches (13) (Error! Reference source not found.), set an arbitrary
data word.
Press the SET/STOP button (15) (Error! Reference source not found.). The set
information (8 bit) is recorded in a parallel way in shift registers (11) (Error! Reference
source not found.). Make sure, that LED-s (3) (Error! Reference source not found.) of
respective switches which are on (logical level “1”), are flashing on. And the remaining
LED-s are not flashing on.
Put the switch MODE (14) (Error! Reference source not found.) into the position
TRANSMIT MODE. The transmission of the successive bits starts: at first the eighth bit is
being transmitted and it continues until the first bit, and later the process of
transmission of successive bits is continued in a cyclic way. Make sure, that the receiver
LED-s (4), which correspond to flashing LED-s of the transmitter (3) (Error! Reference
source not found.) are flashing, and the remaining LED-s are not flashing.
7. Reposition the binary information switches of the transmitter (13) (Error! Reference
source not found.) into different positions through visual examination of the respective
LED-s of the transmitter and the receiver, and make sure, that the information is being
transmitted without distortions.
Investigation of the availability of the fronts (positive one, while transmitting “1” and
negative ones at “0”) using a Scope while transmitting Manchester signals.
8. Launch the Scope using the NI instruments panel. Select SCOPE CH0 in Channel 0
Settings section of Source menu and make sure that CH1 is enabled (Fig.Error! No text
of specified style in document.-2). Then click the Run button on the oscilloscope.
Apply the following basic settings (Fig.Error! No text of specified style in
document.-2).
 CH0 Scale, Volts/Div. – 2V,
 Time-base – 100μs,
 Trigger Type - «Edge»,
 Trigger Level – 1V,
 Horizontal position – 10%
Fig.Error! No text of specified style in document.-2. Preset adjustments of Scope
9. Put all binary switches (13) (Error! Reference source not found.) to “0”
10. Connect CH0 channel probe to the check point DATA (8) (Error! Reference source not
found.). A 100 microsecond width impulse shall arrive on the Scope screen (see
Fig.Error! No text of specified style in document.-3). This is the preamble, which is
necessary for the receiver to precise definition of the beginning of information.
Fig.Error! No text of specified style in document.-3. Preamble model
11. Looking over different combinations of binary information switches, make sure
that after the preamble the remaining eight 100μs-wide sections on the scope
screen correspond to eight information bits.
12. Connect CH0 channel probe to the check point CLOCK (9) (Error! Reference source not
found.). A rectangular 10 kHz TTL signal shall arrive on the Scope screen (Fig.Error! No
text of specified style in document.-4). With the help of that signal the successive
queue of information DATA bits is being transformed into Manchester code.
Fig.Error! No text of specified style in document.-4. Rectangular permanent frequency
signal, with the help of which the successive queue of bits is transformed into the
Manchester
13. With the help of binary information switches of the transmitter (13) (Error!
Reference source not found.) enter 00001001.
14. Connect CH0 channel probe of the Scope to the check point MANCHESTER
CODE (10) (Error! Reference source not found.). The Manchester signal shall
arrive on the screen (Fig.Error! No text of specified style in document.-5).
Fig.Error! No text of specified style in document.-5. Manchester code of information
00001001 at the output of the logical element XOR
Investigation of the presence of fronts in Manchester code signals
15. With the help of a clamp probe connect Scope CH0 channel to the check point RETIMED
DATA (18) (Error! Reference source not found.).
16. Select SCOPE CH1 in Channel 1 Settings section of Source menu and enable CH1
(Fig.Error! No text of specified style in document.-2). Then click Run button on the
oscilloscope. Activate channel CH1 of the Scope and connect the corresponding clamp
probe to check point RETIMED MANCHESTER CODE (17) (Error! Reference source not
found.). Looking over different combinations of the binary information switches make
sure, that the fronts of Manchester code (blue graph) corresponds to the mid points of
the bits (green graph) (Fig.Error! No text of specified style in document.-6). Logical
“1” bits correspond to positive fronts of Manchester code, and the logical “0” bits
correspond to negative fronts.
Fig.Error! No text of specified style in document.-6. Sequential queue of information bits
00001001 (green graph) and the Manchester code signal corresponding to it (blue
graph)
Thus, the synchronization between the transmitter and the receiver during the transmission of
Manchester coded signal is established through the detection of rising or falling edge for each
clock.
Investigation of the availability of additional steps in the Manchester format encoding signals
17. Deactivate the channel CH1 of the Scope and disconnect the corresponding probe.
Increase the trigger level up to 3.5V, and decrease CH0 channel amplitude time-base
down to 1V.
18. Connect CH0 channel probe to the check point JOGGED MANCHESTER CODE (19) (Error!
Reference source not found.).
19. With the help of binary switches (13) (Error! Reference source not found.) set
01010101. Scope screen displays the information signal of Manchester encoding with
additional steps interposed in it (Fig.Error! No text of specified style in document.-7).
Fig.Error! No text of specified style in document.-7. Information signal of Manchester
encoding of information 01010101 with entered additional steps
Thus, the investigation of the availability of additional steps in Manchester code is executed
(See: “Information transmission medium” in theoretical section of lab assignment 3)
Spectral analysis of the signals for revealing the ability of minimization of the spectrum of
transmitted signals
20. Stop the Scope by pressing the Stop button on the Scope software panel
21. From the NI instruments panel activate the spectrum analyzer (DSA) and set the
following options as in the Fig.Error! No text of specified style in document.-8: and
select the following modes:
 Frequency band – 20000 GHz,
 Trigger type – «Edge»,
 Trigger level – 1V,
 Units -put on Linear.
Fig.Error! No text of specified style in document.-8. Preset tuning of spectrum analyzer
22. Click the Run button on the DSA
23. Connect the probe of CH0 channel of the analyzer to the check point RETIMED DATA
(18) (Error! Reference source not found.).
24. Set up all binary switches (13) (Error! Reference source not found.) to “0” and, make
sure, observing the analyzer screen, that the NRZ signal spectrum includes spectral
components in wide frequency band (Fig.Error! No text of specified style in
document.-9).
Fig.Error! No text of specified style in document.-9. NRZ signal spectrum at the
combination of all switches on logical “0”
25. Connect CH0 channel probe of the analyzer to the check point RETIMED MANCHESTER
CODE (17) (Error! Reference source not found.) and make sure, that the Manchester
encoding signal spectrum, apart from low frequency component from 0 to 1000 Hz, has
an explicitly expressed component on a coding frequency 10 KHz (Fig.Error! No text of
specified style in document.-10). The presence of low frequency component in
Manchester signal spectrum is explained by the fact, that the information is transmitted
in a cyclic way, i.e. after the transmission of 8 bits of information after a certain period
of time a new transmission of 8 bits starts. This time exceeds several times the
transmission time of information pack, which is leading to the appearance a low
frequency component in the spectrum.
Fig.Error! No text of specified style in document.-10. The spectrum of Manchester signal
at the combination of all switches on logical “0”
26. Set all binary switches (13) (Error! Reference source not found.) to “1”.
27. Connect the probe of analyzer channel CH0 to the check point RETIMED MANCHESTER
CODE (17) (Error! Reference source not found.) and make sure, that Manchester signal
spectrum has an explicitly expressed spectral component on a 10 KHz frequency
(Fig.Error! No text of specified style in document.-11).
Fig.Error! No text of specified style in document.-11. The spectrum of Manchester signal
at the combination of all switches for logical “1”
28. Connect the CH0 probe of the analyzer to the RETIMED DATA check point (18)
(Error! Reference source not found.) and make sure that NRZ signal spectrum
includes spectral components in wide range of frequencies (Fig.Error! No text of
specified style in document.-12).
Fig.Error! No text of specified style in document.-12. NRZ signal spectrum at the
combination of all switches for logical “1”
Thus, during the transmission of the sequence of logical zeros and ones the NRZ signal
spectrum in a range from 0 to 10KHz has a wide range of spectral components, and the
Manchester encoding format signal has a distinctly expresses maximum at 10KHz.
29. Look over different combinations of binary switches (13) (Error! Reference source not
found.), over watch the signal spectrum from both check points. At that note, the rage
of spectral components as NRZ signals, as well as Manchester encoding signals does
not depend on transmitted data.
Thus, Manchester coding is supporting also another principle of the encoding, namely
“Minimization of the bandwidth of signal spectrum”.
30. Close the analyzer.
The investigation of differential character of the Manchester encoding. Artificial noise
generation and the test of correctness of information transmission.
31. Click the Run button to launch the Scope and set the following parameters:
 CH0 Scale, Volts/Div. – 1V,
 Time Base – 500us,
 Trigger Type - “Edge”,
 Trigger Level – 2.5V,
 Horizontal position – 10%
32. Connect the CH0 channel probe to the check point TP4 (Error! Reference source not
found.).
33. From NI instruments panel, launch the functional generator (FGEN) and select the
following modes:
 Frequency – 1000Hz,
 Amplitude – 2V (Fig.Error! No text of specified style in document.-13)
Fig.Error! No text of specified style in document.-13. Preparatory adjustments of the
functional generator
34. Click the Run button on the FGEN.
35. Track down the Manchester code signal on the oscilloscope screen and note, that it
acquired a shape, superimposed on a sinusoid (Fig.Error! No text of specified style in
document.-14).
Fig.Error! No text of specified style in document.-14. Manchester encoding signal
superimposed on a sinusoid
36. Check the flashed LED-s of the transmitter and receiver and make sure, that the
information is being transmitted without losses.
37. Changing the types of the signals of the functional generator (Triangle, Square)
(meanwhile observing the oscilloscope screen) and rearranging the switches of binary
information (13) (Error! Reference source not found.) in different positions convince
yourself, that the transmitted information is received without distortions.
Thus, the stability of the transmitted through network cable Manchester code with respect to
external inductions (noises) is verified.
38. Close FGEN
39. Close the Scope
40. Press the SET/STOP button, in order to stop the information transmission.
41. Set the PROTOTYPING BOARD POWER switch into the OFF position and close the lab
software panel.
Test Questions
1. List the basic principles of signal encoding.
2. Through which characteristics of the signal format Manchester encoding ensures the
possibility of synchronization?
Answers
1. The basic principles the signal encoding are the following:
 Possibility of synchronization between the transmitter and the receiver
 Minimization of the signal spectrum bandwidth
 Noise immunity
The synchronization during the transmission of Manchester coded signal is established through
the detection of rising or falling edge for each clock