Serial Communications Standards Ch. 3.pptx

Serial Communications Standards Ch. 3 Sample Footer Text Serial Communication s Standards • We have already introduced the concept of serial communications, the placing of one bit after another onto a single media channel • This chapter focuses on three Electronic Industries Alliance /Telecommun...

Serial Communications Standards Ch. 3 Sample Footer Text Serial Communication s Standards • We have already introduced the concept of serial communications, the placing of one bit after another onto a single media channel • This chapter focuses on three Electronic Industries Alliance /Telecommunications Industry Association serial communications standards: numbers 232, 422, and • Serial interface to the PC is being accomplished by newer and much faster technologies, so we will also focus on four PC-based standards that will impact industrial use and automation applications: USB 2.0, FireWire , SATA, and PCIe 01/24/2024 2 Sample Footer Text Basic Concepts • Digital communication is the exchange of binary data between digital devices • The two communicating devices might be physically local to each other or might be far enough apart that some form of intervening telecommunications equipment is needed to enable the communica-tions • The internal voltage-based representation of binary bits within a digital device may be unsuitable for interfacing with the communications channel medium or telecommunications equipment and, thus, some form of signal conversion may be required 01/24/2024 3 Sample Footer Text Definitions • Understanding how data communication equipment and data terminal equipment are defined is essential to any discussion of data communications • From the “dumb” hardware devices, dominant in the 1960s, to today’s software interfaces, these terms are used throughout data communications • In many early applications of digital communications, there was a need to use existing telecommunications infrastructure and/or technology to create a communications channel when the communicating devices were physically widely separated • Data terminal equipment means the end device that sends data to another DTE 01/24/2024 4 Sample Footer Text TIA/EIA Standards • In general, the TIA/EIA serial standards specify the electrical and/or mechanical interface between the DCE and the DTE • The TIA/EIA serial standards only deal with the digital signals between DTEs, DCEs, and other devices • Any discussion of the serial transmission digital data interface between DTE and DCE starts with one of the most widely used digital standards ever developed: the Electronic Industries Alliance 232, which is now in its F version 01/24/2024 5 Sample Footer Text TIA/EIA-232-F • The TIA/EIA-232-F standard is for the interface that makes possible the connection between a DTE and a DCE by employing serial binary data interchange • When this standard was first conceived around 1962, the DTE was either a teletypewriter or a dumb terminal and the distant end DTE was probably a computer • At that time, the standard was originally intended to describe the interface between a modem and a teleprinter —nothing more • Up through RS-232-C , the standard specified only that there be a 25-pin connector and only described the 25 pins and their actions 01/24/2024 6 Sample Footer Text TIA/EIA-232-F • Although TIA/EIA-422 and 423 are now in place, EIA449 apparently never really caught on and RS-232-C continued to be used, even at 19.2 Kbps • Today it is not unusual to see two computers, or a computer and an intelligent device, communicating over a EIA-232 circuit at bit rates of 115,200 bps • The E version brought TIA/EIA-232 in line with International Telecommunications Union V.24 and V.28 and ISO 01/24/2024 7 Sample Footer Text EIA-449: Interface Standard • In contrast to RS-232, EIA-449 used the EIA-422 and EIA-423 standards for media and electrical descriptions • EIA-449 described only the pins, definitions, connector specifications, and functions and referred to EIA-422 and EIA-423 whenever electrical connections to the media interface were described • EIA-449 was originally intended to phase out RS-232 but EIA-449 itself has been replaced by EIA-530 for circuits above 20 Kbps • As an interface may include more than point-to-point circuits, the newer standards tend to describe just the interface’s physical and synchronization characteristics • Two electrical interface standards now in place are TIA/EIA-422 and TIA/EIA 01/24/2024 8 Sample Footer Text EIA-449: Interface Standard • The standard calls for a +200 mV to + 6 V signal, with the most positive condition being the logic 0 state • Noise is normally found in the common mode , but the balanced line uses differential inputs and outputs, which by nature have a high common mode rejection ratio , so noise is reduced as a factor in signal quality • A differential transmitter puts the transmitted signal on one line and a polarity-inverted copy of the transmitted signal on the other 01/24/2024 9 Sample Footer Text Interface Signal Functions • This knowledge is useful for determining whether a serial interface is operating correctly • Several of the signals in the various EIA standards were used specifically for handshaking • Hardware handshaking enabled devices to signal their state and ability to receive to the corresponding device at the other end of the channel • The most common interface between a computer and, for example, a telephone modem is an EIA-232 connection with all of the hardware handshaking signals 01/24/2024 10 Sample Footer Text Ensuring Operability • In most PCs , the serial COM ports are connected to a special integrated circuit, called a UART, that can send and receive 8-bit data values via an EIA-232 circuit • These UART chips interface to the various data and handshaking signals of the EIA-232 circuit and allow software to examine and set/clear the applicable signals • Sent from the DCE to the DTE, this signal determines whether the DCE is in the DATA mode and ready to communicate and whether the DCE is authorized to set up a link once it has detected ringing • As long as DTE Ready is TRUE, then data will be transferred to the DTE • In practice, hardware flow control depended on only one set of the two handshaking pairs to be used for handshaking 01/24/2024 11 Sample Footer Text Ensuring Operability 01/24/2024 • Circuit 133) in the E version of EIA-232, RTS was set to TRUE as a ready to receive signal, rather than having a relationship with CTS 12 Sample Footer Text Synchronous Communicatio n • If a device uses a UART for serial communications , then it is performing asynchronous serial communications in which there can be gaps between data being sent • The data is sent as one or more octets , with a special start bit and stop bit appended to each octet at the sending end by the transmitting UART • The HDLC protocol is a commonly used synchronous protocol, in which there is a unique 8-bit pattern called a flag character used to identify the start and end of a message • Specialized transmitting and receiving hardware is needed for synchronous communications because the UART chip in a typical PC cannot support synchronous transmission • Synchronous data transmission is commonly found today in all high-speed local area networking technologies 01/24/2024 13 Sample Footer Text PC Serial Communications • Just as EIA-232 use was greatly expanded by the personal computer , other buses, internal and external to the computer, have also appeared • For a long time, external line speeds required only the EIA232, then the EIA-422/485 connections or perhaps the SCSI extended bus • However, much higher speeds and the constraints media imposed on these signals required a rethinking of the serial signal organization and the software that drives it 01/24/2024 14 Sample Footer Text Universal Serial Bus • The Universal Serial Bus was originally developed in 1995 by industry-leading companies • The concept was to define an external expansion bus that made adding peripherals to a PC as simple as plugging in a network jack • The design goals were low cost and true “plug-and-play” operation • Figure 3-14 illustrates a laptop computer with a root hub showing connections to a USB hub, a printer, a mouse, a wireless access point, and a ready-to-connect flash drive • It is backward-compatible with the 1.x and 2.0 version devices that run at either 480 Mbps , 12 Mbps , or 1.5 Mbps • USB version 3 operates at a higher speed and is the newest release • There are PCI Express cards available to add USB 3.0 hardware to PCs 01/24/2024 15 Sample Footer Text Universal Serial Bus • The USB attachment cable may have either a Type-A or a Type-B connector • A Type-A port is usually found on the PC, and Type-B ports are generally on the devices 01/24/2024 16 Sample Footer Text IEEE 1394 • IEEE 1394 is a fast external bus standard that supports data transfer rates of up to 400 Mbps and 800 Mbps • The standard allows for rates of 1.6 and 3.2 Gbps • IEEE 1394c-2006 IEEE 1394c-2006 was published on June 8 • IEEE 1394-2008 This classification of products uses the S1600 and S3200 modes that compete with USB 3 • IEEE 1394d – Proposed This was a project to add single mode fiber as an additional transport medium to FireWire • IEEE 1394 supports isochronous data, which means it delivers data at a guaranteed rate • The IEEE 1394 protocol uses an 8B/10B signaling scheme, where 8-bit combinations are represented by 10-bit patterns 01/24/2024 17 Sample Footer Text SCSI • SCSI has been around since • SCSI has moved in the past several years from a parallel configuration to a serial connection, although the Ultra 320 parallel still transfers data at a higher rate over a longer distance than the SCSI serial versions • SCSI’s primary use is as a multiple disk interface, particularly in fault-tolerant arrays, such as Redundant Array of Independent Disks in configurations as RAID 10 or RAID 01/24/2024 18 Sample Footer Text SATA • SATA replaces the parallel ATA for connecting EIDE drives to PC motherboards • SATA currently has data rates from 0.5 Gbps and 16.0 Gbps, however, these data rates have a maximum length of 1 m ; therefore, SATA should not be considered for long external peripheral connections • This chapter considered some of the more commonly used serial data communications interface standards • This chapter has shown how a standard, RS-232, now TIA/EIA-232-F and originally rather limited in scope, has kept pace with technology • EIA-530 is a mechanical standard for a balanced-toground signal system that uses a connector identical to RS-232, except in pinouts 01/24/2024 19