datacom module 5 (uart, usrt, serial interface, modem)

Module 5Fundamental Concepts of

Data Communications(UART, USRT, Serial Interface, MODEM)

Chapter 22

Electronic Communications Sytems , Fifth Editon

By: Wayne Tomasi

ECE @Saint Louis University, Baguio City1

Prepared by: Engr. Jeffrey Des B. Binwag

Universal Asynchronous Rx/Tx

ECE @Saint Louis University, Baguio City 2

Universal Asynchronous Rx/Tx


UART FUNCTIONS

• Parallel-to-serial at the Tx and Serial-to-parallel conversion at the Rx

• Error detection

• Framing

• Formatting

• Status monitoring

• Voltage level conversion/matching

• Bit and character synchronizationECE @Saint Louis University, Baguio City 4

UART Control Word


UART Transmitter


UART Receiver


UART Receiver Start-bit Verification


EXAMPLES1. Write the TSO bit sequence out of a UART transmitter that

encodes the message ECESpWEEK using a control word of DA Hex.

2. Decode the following bit sequence using a control word CE Hex and determine if any errors occur. Which characters contain errors? What is the message without corrections? What is the most likely message?

1111 1111 1111 0111 0101 1111 0100 0001 1011 1111 0101 0101 1011 1111 0100 0001 1011 1111 1111 0111 0001 1011 0010 0001 1011 0101 0001 1111 1111 0101 0101 1011 0100 0001 1011 0100 0001 1111 1111 1111 0010 0111 1011 1111 0000 0111 1011 1111 1111 0100 0111 1011 0101 0111 1111 1111 1111 1111 1111 1111


USRT Sampling Error


USRT FUNCTIONS

• Parallel-to-serial at the Tx and Serial-to-parallel conversion at the Rx

• Error detection

• Synchronization

• Formatting

• Status monitoring

• Voltage level conversion/matching

• Bit and character synchronizationECE @Saint Louis University, Baguio City 11

Serial Interface• A communication interface between two digital

systems that transmits data as a series of voltage pulses down a wire.

• Originally designed as the primary link between Data Terminal Equipment and its Data Communication Equipment.

• Now used for multiple applications requiring serial-by-bit transmission between digital equipment and peripherals.

• The first standardized serial interface was published as a recommended standard RS-232 by the EIA in 1962.


Serial Interface


Serial Interface

• A serial interface standard must provide the following:

1. A specific range of voltages for transmit and receive signal levels

2. Limitation for the electrical parameters of the transmission line.

3. Standard cable and cable connectors.

4. Functional description of each signal on the interface.


RS-232 Serial Interface• Officially named Interface Between Data Terminal

Equipment and Data Communications Equipment Employing Serial Binary Interchange.

• Introduced by the EIA at a time when there was considerable diversity in the serial interfaces manufactured by different data communication equipment providers.

• It specifies the mechanical, electrical, functional, and procedural descriptions for the interface between DTEs and DCEs.

• Similar to the ITU-T V.28 electrical specifications and the V.24 functional description designated for transmission up to 20 kbps over a maximum distance of 50 ft.


RS-232 Physical Characteristics

• Cable. A sheath containing 25 wires with two connectors called the DB25P-compatible male connector (plug) on one end and a DB25S-compatible connector (receptacle) on the other end designed to transmit synchronous or asynchronous data.

• DB9P and DB9S connectors can alternately be used for asynchronous data transmission.


• DB25 and DB9 Pinout


RS-232 Electrical Characteristics

• Driver load impedance: 3kΩ – 7k Ω

• Maximum capacitive load: 2500 pF

• Maximum data rate: 20 kbps

• Maximum length: 15 m (50 ft.)

• Logic voltages:


DATA SIGNALS CONTROL SIGNALS

LOGIC ‘1’ LOGIC ‘0’ ENABLE DISABLE

DRIVER -5 to -15 +5 to +15 +5 to +15 -5 to -15

TERMINATOR -3 to -25 +3 to +15 +3 to +15 -3 to -25

RS-232 Electrical Characteristics


RS-232 Equivalent Circuit

RS-232 Functional Characteristics


RS-232 Procedural Characteristics


Null Modem Connection

RS-232 Procedural Characteristics


Example. Draw the timing diagram for a null modem connection with the following specifications:

• RTS/CTS Delay : 40 mS for Switched Carrier

20 mS for Cont. Carrier

• RLSD Delay : 20 mS ON, 10 mS OFF

• Primary Carrier Option : Switched Carrier and RTS

• Secondary Carrier Option : Switched Carrier and RTS

• Propagation Time (Downstream) : 20 mS

• Propagation Time (Upstream) : 20 mS

• Secondary Turnaround Time : 40 mS

• Secondary Message Length : 40 mS

• Primary Message : 60 mS

• Primary On time : 0 mS

Other Serial Interface Standards• The RS-449 standard was designed in 1977 as a 37 wire

cable to replace the RS-232 interface.

• The RS-449 circuits were divided into two categories: Category I were circuits (pins) compatible with the RS-232 standard while the remaining circuits were under Category II.

• The RS-449 Standard specifies 10 circuits not specified in the RS-232 standard: LL(10), RL(14), SF(16), TM(18), RC(20), IS(28), SS(32), NS(34), SB(36), SC(37).

• The RS-422 and RS-423 specify the electrical specifications of the RS-449 serial interface.


Other Serial Interface Standards

• The RS-422A standard specifies a balanced interface cable capable of spanning 15 meters at 10 Mbps data rate but could extend to 1200 meters at slower speeds.

• The RS-423A standard specifies a balanced interface cable capable of operating at a maximum rate of 100 kbps and maximum length of 90 meters.


Other Serial Interface Standards

• The RS-530 standard was introduced by the EIA in 1987. This cable uses the same 25-pin connector of the RS-232 and uses the electrical specifications outlined by either the RS-422A or the RS-423A standards.

• The RS 530 standard operates at data rates between 20kbps and 2 Mbps.


Data Communication Modems

• Data Communication Modems. Devices principally designed to interface computers, computer networks and other digital terminal equipment to analog communication facilities necessary when transmitting signals over long distances.

• Modems perform digital to analog conversion prior to modulation at the transmitter and analog to digital conversion after demodulation at the receiver.

• Telephone Loop or POTS Modems. Modems used to interface DTEs through a serial interface to standard voice-band telephone lines at data rates from 300 bps to 56 kbps.



• Data Communication Modem Block DiagramECE @Saint Louis University, Baguio City 28


• Modem Specifications.


Data Communication Modems• Modem Synchronization. Achieved by sending a special

internally generated bit pattern called the training sequence to synchronize/ train the receive modem at the other end of the communications channel. The training sequence accomplishes one or more of the following:

– Initializes the communication channel (i.e. disabling echo and AGC gain)

– Verifies continuity

– Initializes receive modem descrambler circuits

– Initializes receive modem automatic equalizers

– Synchronize receive carrier to the transmit carrier

– Synchronize receive clock to the transmit clock


Data Communication Modems• Modem Equalizers. Circuits designed to reduce the phase delay

and amplitude distortion inherently present on telephone communications channels.

• Compromise Equalizers. Located at the transmitter modem to provide pre-equalization by shaping the transmitted signal (altering delay and gain characteristics) before the signal reaches the telephone line. May affect: 1. Amplitude Only, 2. Delay Only, 3. Amplitude and Delay, or 4. Neither Amplitude nor Delay.

• Adaptive Equalizers. Located at the receiver modem to provide post-equalization to the signal by automatically adjusting gain and delay characteristics to compensate for phase and amplitude impairments introduced by the communication channel.



• ITU-T Modem Recommendations. V-series of recommendations published by the ITU-T in the late 1980s as transmission standards for data modems outside the United States.

• GROUP WORK: Make a comparative table of the important V-series standards mentioned by Tomasi namely: V.29, V.32, V.32bis, V.32terbo, V.32(Vfast), V.33, V.34+, V.42, V.90, V.92. Specify important parameters such as: year of publication, transmission speed, maximum cable length, type of modulation, error coding, etc.


Data Communication Modems• ITU-T V-Series Standards Summary: (Alcantara, Austria, Datic, Ismael, Quiray)


ITU-TStandard

Data Rate(bps)

No. of

Bits

BaudRate

OperatingMode

Modulation CarrierFrequency

Error Coding/Other

Characteristics

V.29(1988)

9600 4 2400 FullDuplex

16 QAM 1700 Pingpong;StatisticalDuplexing

V.32(1988)

960024004800

5 2400 FullDuplex

QAM/TCM

1800 Trellis Encoding;Echo Cancellation

V.32bis(1991)

14400;1220096004800

6 2400 FullDuplex

QAM/TCM

1800 Fall-forward and Fall-back Features;

Data Compression

V.32Terbo(1993)

1920014400;1220096004800

6 2400 FullDuplex

QAM/TCM

1800 Adaptive Speed Levelling; Fall-forward and Fall-back features;

Data Compression



ITU-TStandard

Data Rate(bps)

No. of

Bits

BaudRate

OperatingMode


Error Coding/Other

Characteristics

V.32V.fast(1994)

28800 8 3429 FDX/ HDX PCM 1800 Nonlinear Coding; Multidimensional

Coding; Constellation Shaping; Reduced

Decoder Complexity; Precoding of Data; Line

Probing

V.33(1988)

14400 6/1Info/redundant

2400 FDX 128 QAM64 QAM

TCM

1800 Trellis Coding

V.34+(1996)

288003120033600

5 3429 FDX/HDX

Assymetric

TCM 1800 MSE Fallback or Fall Forward control; Echo

Cancellation



ITU-TStandard

Data Rate(bps)

No. of

Bits

BaudRate

OperatingMode


Error Coding/Other

Characteristics

V.42(1988)

28800 6 2400 FDX QAM 1800 Asynchronous to Synchronous

Conversion; ErrorDetection and

Correction; LAPM

V.90(1998)

56000(Rx)

33600(Tx)

5to8

3200or

8000

FDX PCM/TCM

1800 Asymmetrical Data Transmission

V.92(2000)

56000(Rx)

48000(Tx)

5to8

8000 FDX PCM 3000 Asymmetrical Data Transmission; Faster call

set-up capabilities; Incorporation of a hold

option

Thank You!

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For the USB 3.0 discussion


datacom module 5 (uart, usrt, serial interface, modem)

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