Lab6
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Experiment No. 6
Study of Time Division Multiplexing (TDM)
TIMING AND SYNC.
MARKER
AUDIO 1 HS 1
AUDIO 2 HS 2
SWITCHES K1 TO K4
M U L T I P L E X E R
LINE CODING
EXPANSION CHANNELS FIBER OPTIC TRANSMITTER AND RECEIVER SYSTEM
AUDIO 1 HS 1
AUDIO 2 HS 2
LEDs D5 TO D8
EXPANSION CHANNELS
D E U L T I P L E X E R
RECEIVED DATA LINE DECODING MARKER RECEIVED CLOCK TIMING AND SYNC.
BLOCK DIAGRAM FOR TIME DIVISION MULTIPLEXING
JUMPER SETTING DIAGRAM FOR EXPERIMENT NO. 6
1
2
Audio 1 to Codec 1 I/P
3
4
Ext-Analog to Codec 1 I/P 2
Emitter of Q2 (2N2907)
1
Cathode of SFH 756V Collector of Q1 (2N3904)
3
JP1
4
Cathode of SFH 450V JP8
1
2
Audio 2 to Codec 2 I/P
3
4
Ext-Analog to Codec 2 I/P
JP2
+5V
1
SFH 756V Anode
2
+9V
3 JP10
2
1
Audio 1 to Audio 1 Audio 2 to Audio 1 Audio 1 to Audio 2
8
7
Audio 2 to Audio 2
JP3 2.048 MHz
2
1
256 KHz EXT-TTL Manchester Coded Data
7
8
Digital Buffer I/P for LED SFH 756V
JP4 1
JP5
2
Manchester Coded Data Received From Photodetector Manchester Decoder Circuit I/P
3
Manchester Coded Data (Directly)
SWITCH SETTING DIARAM FOR EXPERIMENT NO. 6 Switch Settings for Marker
SW1
8
SW2 ON
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
ON
7
6
5
4 3 2 1
L
SW3
ON
M
L
8
7
6
5
4 3
2 1
M SW4
ON
Switch Settings For Audio Channels in Time Zone M
L
4 3 2 1
ON SW5 Audio 1 Tx setting
M 4
L 3
2
1
ON SW7 Audio 2 Tx setting
M
L
M
L
SW6
ON
SW8
ON
1 2 3 4 Audio 1 Rx setting
1 2 3 4 Audio 2 Rx setting
Switch Settings For Manchester Coder
4 3 2 1
ON
SW9
SW9-2
SW9-1
Data for coding Clock for coding
0
0
TDM data
2.048 MHz
0
1
128 KHz freqn.
256 KHz.
1
0
64 KHz. freqn.
256 KHz.
1
1
32 KHz freqn
256 KHz.
FIBER TRAINER BLOCK SCHEMATIC Binary Weighted Clock at 2.048MHz Marker_1_Trans
BUFFER
Marker_2_Trans
Xilinx_Trans
BUFFER
4-bit KEY Input
Audio Channel-
Audio Interface and Codec
Audio Channel-
Audio Interface and Codec
Audio-1 channel set-up
Audio-2 channel set-up
Audio-1 channel set-up
Audio-2 channel set-up
Analog/Digital Line Interface for SFH 450/756 O F C I N T E R F A C E
Xilinx_Rec Marker_1_ Rec Marker_2_Rec
Analog/Digital Line Interface for SFH 350/551
BUFFER BUFFER
4-bit LED Array
Mono-Shot Clk Detector
Reference
Device
Function
Xilinx_Rec / Xilinx_Trans
XC9572
Binary weighted clock Marker_X_X Audio Interface & Codec Interface for SFH XXX Mono-shot 4-bit I/O OFC Interface Buffer
Crystal DIP Switch HD44233 Amp/Gates 74121 Switch/LED Plastic Fiber 74245
Manchester Encoding/Decoding, 32-channel TDM, Clk/Data Recovery Base Frequency Marker for frame identification A/D & D/A sampling of input voice Signal Compatibility Clock Separation Data Transmission Verification Transmission Media Buffering to inputs
LEGEND
EXPERIMENT NO. 6 NAME Study of Time Division Multiplexing
OBJECTIVE The objective of this experiment is to study simultaneous transmission of several signals using synchronous time division multiplexing.
THEORY In case of communication systems, signals, which are transmitted usually, carry voice or video information with them & are interpreted by human eye or ears, which has slow response. Persistence of vision as well as of hearing has given rise to the concept of time division multiplexing. In time division multiplexing various signals are sampled & transmitted for a fixed duration of time one after the other. At the receiving end these signals are extracted in the same order & form of transmission. To implement this scheme we have used 32 channel digital multiplexer at transmission end with clock generator for timing of signals. One channel is reserved for marker transmission, two channels for voice data transmission, four channels take their inputs from four data switches & other channels are available as expansion channels for user. Each channel has a data rate of 64 Kbits / Sec. This multiplexed data is then Manchester coded & fed as digital data to the transmitter. The received digital data is first Manchester decoded & passed through a clock recovery circuit & then demultiplexed giving each signal separate in its original form & shape.
CIRCUIT DESCRIPTION The block diagram given in fig 6.1 clearly indicates the circuit flow. 1. The timing & synchronization circuit generates three clock frequencies -2.048MHz, 256 KHz and 8 KHz. These are generated for the complete time division multiplexed transmission of the data from 32 channels. The data bits are transmitted at the rate of 2.048 MHz. Each channel is selected for on period of 1/256 KHz. Thus per channel 8 bits of data is transmitted. The channel selection frequency is 8 KHz. Thus a single frame of 32 channels exists for a period of 125 uS. 2. The marker setting is achieved using switches SW1 & SW2. The two eight bit markers are alternately transmitted at the start of each frame.
TRANSMITTER SECTION: 3. The voice signals from telephone handsets are processed and applied to CODEC. The analog to digital conversion process inside the CODEC samples the signal at a frequency of 8 KHz and this sampled digitized data is applied to the multiplexer input. 4. The marker, the data bits from two audio channels, data from four switches and those from expansion channels are multiplexed. The multiplexed data is Manchester coded and transmitted through the fiber.
RECEIVE SECTION: 5. The received data is Manchester decoded to separate clock and data (The detailed explanation of Manchester coding and decoding is given in expt no. 8) and is applied to a demultiplexer.
6. Same received data is applied to the marker detection circuitry where low going pulses are generated corresponding to the each marker received and are used as synchronizing signal for timing circuitry. 7. The demultiplexer forms the data distribution system from where the samples are separated and are applied to corresponding channels. 8. The switch channels directly drive the LEDs and the decoded voice data is again applied to the CODEC. The converted analog signal is then interfaced with telephone.
EQUPMENTS Experimenter Kit 20 MHz dual Trace Oscilloscope 1 Meter Fiber Cable Telephone Handset
PROCEDURE 1.
Connect 1 meter optical fiber cable between LED SFH756V & detector SFH551V as explained in earlier experiments to form 660 nm digital link. 2. Assure the jumper and switch settings as shown in the jumper/switch block diagram. 3. Set Marker1 & Marker2 each for bit pattern shown in the diagram using SW1 & SW2 respectively. Observe the time division multiplexed data at TP10 on CRO. 4. Carefully observe the time duration for which each channel is selected. Observe & measure the frame period. 5. Change the marker setting & observe the multiplexed data. Observe how both the markers are alternately transmitted in each frame. 6. Press either of the Topaz keys (K1 - K2) and observe how data is transmitted in the corresponding time slot. Thus, you can observe the signals at different points of the transmitter section. 7. Observe the Manchester coded data at TP13. This data is transmitted through the fiber. The received data, which is still in Manchester coded form, is available at TP21. 8. Observe the data transmission by pressing keys (K1-K4) & observing the corresponding LEDs (D5-D8) lit up. The recovered data at the receiver is available at test point TP16. 9. Hear the voice input at the mouthpiece being looped back through the fiber to the corresponding earpiece. The voice input at one mouthpiece cannot be heard at the earpiece of another handset. Observe this TDM effect. 10. Change the jumper connections of JP8 to cross couple the handsets; refer to the jumper diagram. This establishes a cross link between the two receivers. The voice input at the mouthpiece of one handset can now be heard at the earpiece of another handset. 11. The Time Division Multiplexing phenomenon can further be studied by taking following observations: In our scheme of TDM we have used two audio and five expansion channels. One Audio channel ‘Audio-1’ is mapped in first 16 channels and can be set any where in between channels 6 to 15 (channels 0 to 5 are reserved for marker and four key switches.). This is achieved using the 4 bit switches SW5 and SW6 as shown in the block diagram. Change the switch settings for Sw5 and observe how audio data moves in different time slots. To receive the data in same time slot you must set the SW6 same as that SW5. SW5 and SW6 are to be down counted in binary sequence for channels 0 to 15, i.e. 1111-> CH0, 1110 --> CH1,… 0000--> CH15. Second audio channel ‘Audio-2’ is mapped in next 16 channels and can switched in time slot using switches SW7 and SW8 same as for audio channels 1.
Study of Time Division Multiplexing (TDM)
TIMING AND SYNC.
MARKER
AUDIO 1 HS 1
AUDIO 2 HS 2
SWITCHES K1 TO K4
M U L T I P L E X E R
LINE CODING
EXPANSION CHANNELS FIBER OPTIC TRANSMITTER AND RECEIVER SYSTEM
AUDIO 1 HS 1
AUDIO 2 HS 2
LEDs D5 TO D8
EXPANSION CHANNELS
D E U L T I P L E X E R
RECEIVED DATA LINE DECODING MARKER RECEIVED CLOCK TIMING AND SYNC.
BLOCK DIAGRAM FOR TIME DIVISION MULTIPLEXING
JUMPER SETTING DIAGRAM FOR EXPERIMENT NO. 6
1
2
Audio 1 to Codec 1 I/P
3
4
Ext-Analog to Codec 1 I/P 2
Emitter of Q2 (2N2907)
1
Cathode of SFH 756V Collector of Q1 (2N3904)
3
JP1
4
Cathode of SFH 450V JP8
1
2
Audio 2 to Codec 2 I/P
3
4
Ext-Analog to Codec 2 I/P
JP2
+5V
1
SFH 756V Anode
2
+9V
3 JP10
2
1
Audio 1 to Audio 1 Audio 2 to Audio 1 Audio 1 to Audio 2
8
7
Audio 2 to Audio 2
JP3 2.048 MHz
2
1
256 KHz EXT-TTL Manchester Coded Data
7
8
Digital Buffer I/P for LED SFH 756V
JP4 1
JP5
2
Manchester Coded Data Received From Photodetector Manchester Decoder Circuit I/P
3
Manchester Coded Data (Directly)
SWITCH SETTING DIARAM FOR EXPERIMENT NO. 6 Switch Settings for Marker
SW1
8
SW2 ON
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
ON
7
6
5
4 3 2 1
L
SW3
ON
M
L
8
7
6
5
4 3
2 1
M SW4
ON
Switch Settings For Audio Channels in Time Zone M
L
4 3 2 1
ON SW5 Audio 1 Tx setting
M 4
L 3
2
1
ON SW7 Audio 2 Tx setting
M
L
M
L
SW6
ON
SW8
ON
1 2 3 4 Audio 1 Rx setting
1 2 3 4 Audio 2 Rx setting
Switch Settings For Manchester Coder
4 3 2 1
ON
SW9
SW9-2
SW9-1
Data for coding Clock for coding
0
0
TDM data
2.048 MHz
0
1
128 KHz freqn.
256 KHz.
1
0
64 KHz. freqn.
256 KHz.
1
1
32 KHz freqn
256 KHz.
FIBER TRAINER BLOCK SCHEMATIC Binary Weighted Clock at 2.048MHz Marker_1_Trans
BUFFER
Marker_2_Trans
Xilinx_Trans
BUFFER
4-bit KEY Input
Audio Channel-
Audio Interface and Codec
Audio Channel-
Audio Interface and Codec
Audio-1 channel set-up
Audio-2 channel set-up
Audio-1 channel set-up
Audio-2 channel set-up
Analog/Digital Line Interface for SFH 450/756 O F C I N T E R F A C E
Xilinx_Rec Marker_1_ Rec Marker_2_Rec
Analog/Digital Line Interface for SFH 350/551
BUFFER BUFFER
4-bit LED Array
Mono-Shot Clk Detector
Reference
Device
Function
Xilinx_Rec / Xilinx_Trans
XC9572
Binary weighted clock Marker_X_X Audio Interface & Codec Interface for SFH XXX Mono-shot 4-bit I/O OFC Interface Buffer
Crystal DIP Switch HD44233 Amp/Gates 74121 Switch/LED Plastic Fiber 74245
Manchester Encoding/Decoding, 32-channel TDM, Clk/Data Recovery Base Frequency Marker for frame identification A/D & D/A sampling of input voice Signal Compatibility Clock Separation Data Transmission Verification Transmission Media Buffering to inputs
LEGEND
EXPERIMENT NO. 6 NAME Study of Time Division Multiplexing
OBJECTIVE The objective of this experiment is to study simultaneous transmission of several signals using synchronous time division multiplexing.
THEORY In case of communication systems, signals, which are transmitted usually, carry voice or video information with them & are interpreted by human eye or ears, which has slow response. Persistence of vision as well as of hearing has given rise to the concept of time division multiplexing. In time division multiplexing various signals are sampled & transmitted for a fixed duration of time one after the other. At the receiving end these signals are extracted in the same order & form of transmission. To implement this scheme we have used 32 channel digital multiplexer at transmission end with clock generator for timing of signals. One channel is reserved for marker transmission, two channels for voice data transmission, four channels take their inputs from four data switches & other channels are available as expansion channels for user. Each channel has a data rate of 64 Kbits / Sec. This multiplexed data is then Manchester coded & fed as digital data to the transmitter. The received digital data is first Manchester decoded & passed through a clock recovery circuit & then demultiplexed giving each signal separate in its original form & shape.
CIRCUIT DESCRIPTION The block diagram given in fig 6.1 clearly indicates the circuit flow. 1. The timing & synchronization circuit generates three clock frequencies -2.048MHz, 256 KHz and 8 KHz. These are generated for the complete time division multiplexed transmission of the data from 32 channels. The data bits are transmitted at the rate of 2.048 MHz. Each channel is selected for on period of 1/256 KHz. Thus per channel 8 bits of data is transmitted. The channel selection frequency is 8 KHz. Thus a single frame of 32 channels exists for a period of 125 uS. 2. The marker setting is achieved using switches SW1 & SW2. The two eight bit markers are alternately transmitted at the start of each frame.
TRANSMITTER SECTION: 3. The voice signals from telephone handsets are processed and applied to CODEC. The analog to digital conversion process inside the CODEC samples the signal at a frequency of 8 KHz and this sampled digitized data is applied to the multiplexer input. 4. The marker, the data bits from two audio channels, data from four switches and those from expansion channels are multiplexed. The multiplexed data is Manchester coded and transmitted through the fiber.
RECEIVE SECTION: 5. The received data is Manchester decoded to separate clock and data (The detailed explanation of Manchester coding and decoding is given in expt no. 8) and is applied to a demultiplexer.
6. Same received data is applied to the marker detection circuitry where low going pulses are generated corresponding to the each marker received and are used as synchronizing signal for timing circuitry. 7. The demultiplexer forms the data distribution system from where the samples are separated and are applied to corresponding channels. 8. The switch channels directly drive the LEDs and the decoded voice data is again applied to the CODEC. The converted analog signal is then interfaced with telephone.
EQUPMENTS Experimenter Kit 20 MHz dual Trace Oscilloscope 1 Meter Fiber Cable Telephone Handset
PROCEDURE 1.
Connect 1 meter optical fiber cable between LED SFH756V & detector SFH551V as explained in earlier experiments to form 660 nm digital link. 2. Assure the jumper and switch settings as shown in the jumper/switch block diagram. 3. Set Marker1 & Marker2 each for bit pattern shown in the diagram using SW1 & SW2 respectively. Observe the time division multiplexed data at TP10 on CRO. 4. Carefully observe the time duration for which each channel is selected. Observe & measure the frame period. 5. Change the marker setting & observe the multiplexed data. Observe how both the markers are alternately transmitted in each frame. 6. Press either of the Topaz keys (K1 - K2) and observe how data is transmitted in the corresponding time slot. Thus, you can observe the signals at different points of the transmitter section. 7. Observe the Manchester coded data at TP13. This data is transmitted through the fiber. The received data, which is still in Manchester coded form, is available at TP21. 8. Observe the data transmission by pressing keys (K1-K4) & observing the corresponding LEDs (D5-D8) lit up. The recovered data at the receiver is available at test point TP16. 9. Hear the voice input at the mouthpiece being looped back through the fiber to the corresponding earpiece. The voice input at one mouthpiece cannot be heard at the earpiece of another handset. Observe this TDM effect. 10. Change the jumper connections of JP8 to cross couple the handsets; refer to the jumper diagram. This establishes a cross link between the two receivers. The voice input at the mouthpiece of one handset can now be heard at the earpiece of another handset. 11. The Time Division Multiplexing phenomenon can further be studied by taking following observations: In our scheme of TDM we have used two audio and five expansion channels. One Audio channel ‘Audio-1’ is mapped in first 16 channels and can be set any where in between channels 6 to 15 (channels 0 to 5 are reserved for marker and four key switches.). This is achieved using the 4 bit switches SW5 and SW6 as shown in the block diagram. Change the switch settings for Sw5 and observe how audio data moves in different time slots. To receive the data in same time slot you must set the SW6 same as that SW5. SW5 and SW6 are to be down counted in binary sequence for channels 0 to 15, i.e. 1111-> CH0, 1110 --> CH1,… 0000--> CH15. Second audio channel ‘Audio-2’ is mapped in next 16 channels and can switched in time slot using switches SW7 and SW8 same as for audio channels 1.
