The common purpose of transmission line drivers and receivers is to transmit data quickly and reliably through a variety of environments over electrically long distances. This task is complicated by the fact that externally introduced noise and ground shifts can severely degrade the data.
The connection between two elements in a system should be considered a transmission line if the transmitted signal takes longer than half its rise or fall time to travel from the driver to the receiver.
The Electronics Industry Association (EIA) and the Telecommunications Industry Association (TIA) have developed several standards to simplify the interface in data communications systems. Previously, EIA labeled the standards with the prefix "RS", which stood for recommended standard. This has been deleted and replaced with TIA/EIA, to help identify the standardizing organizations. The letter suffix represents the revision level of the standard. For example, TIA/EIA-232-F, denotes the sixth revision of RS-232.
All new and revised standards will adopt the new prefix nomenclature of TIA/EIA. Existing standards utilize the prefix that was current at the time the standard was balloted (approved). This includes the familiar RS, EIA, and EIA/TIA prefix.
Single-Ended Data Transmission
In data processing systems today there are two basic means of communication between components. One method is single-ended, which uses only one signal line for data transmission, and the other is differential, which uses two signal lines. See National Application Note number 216 for a list of single-ended data transmission standards from the TIA/EIA.
Differential Data Transmission
When transmitting at very high data rates, over long distances and through noisy environments, single-ended transmission is often inadequate. In these applications, differential data transmission offers superior performance. Differential transmission nullifies the effects of ground shifts and noise signals which appear as common mode voltages on the transmission line. See National Application Note number 216 for a list of differential data transmission standards from the TIA/EIA.
TIA/EIA-232 (RS-232)
The most popular Interface standard in the world is RS-232. RS-232 was first introduced in 1962 and has been widely used throughout the industry. It was developed for single-ended data transmission at relatively slow data rates (20 kbps) over short distances (typically up to ~50 ft.).
TIA/EIA-423 (RS-423)
With the need to transmit data faster and over longer distances, TIA/EIA-423-B, a newer standard for single-ended applications, was established. TIA/EIA-423-B extends the maximum data rate to 100 kbps (up to 30 ft.) and the maximum distance to 4000 feet (up to 1 kbps).
TIA/EIA-422 (RS-422)
TIA/EIA-422-B was defined by the EIA for high-speed data transmission in rugged environments. It allows data rates up to 10 Mbps (up to 40 ft.) and line lengths up to 4000 feet (up to 100 kbps). Drivers designed to meet this standard are well suited for party-line type applications where only one driver is connected to, and transmits on, a bus and up to 10 receivers can receive the data. While a party-line type of application has many uses, TIA/EIA-422-B devices cannot be used to construct a truly multipoint bus. A multipoint bus consists of multiple drivers and receivers connected to a single bus, and any one of them can transmit or receive data. (See RS-485).
TIA/EIA-485 (RS-485)
To meet the need for truly multipoint communications, the EIA established RS-485 in 1983. TIA/EIA-485-A meets all the requirements of TIA/EIA-422-B, but in addition, this standard allows up to 32 drivers and 32 receivers to be connected to a single bus-thus allowing a truly multipoint bus to be constructed. It supports bi-directional half-duplex data transmission.
TIA/EIA-644 (LVDS)
To meet the need for a very high speed interface, the TIA/EIA committee TR30.2 established TIA/EIA-644 in 1995. This electrical standard generically known as LVDS (Low Voltage Differential Signaling) provides all the benefits of differential data transmission and is capable of operating at data rates in excess of 655 Mbps.
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