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Black Box Explains...RS-232.

RS-232, also known as RS-232C and TIA/EIA-232-E, is a group of electrical, functional, and mechanical specifications for serial interfaces between computers, terminals, and peripherals. The RS-232 standard was developed by... more/see it nowthe Electrical Industries Association (EIA), and defines requirements for connecting data communications equipment (DCE)—modems, converters, etc.—and data terminal equipment (DTE)—computers, controllers, etc.) devices. RS-232 transmits data at speeds up to 115 Kbps and over distances up to 50 feet (15.2 m).

The standard, which is functionally equivalent to ITU V.24/V.28, specifies the workings of the interface, circuitry, and connector pinning. Both sync and async binary data transmission fall under RS-232. Although RS-232 is sometimes still used to transmit data from PCs to peripheral devices, the most common uses today are for network console ports and for industrial devices.

Even though RS-232 is a “standard,” you can’t necessarily expect seamless communication between two RS-232 devices. Why? Because different devices have different circuitry or pinning, and different wires may be designated to perform different functions.

The typical RS-232 connector is DB25, but some PCs and other data communication devices have DB9 connectors and many newer devices have RJ-45 RS-232 ports. To connect 9-pin PC ports or RJ-45 to devices with 25-pin connectors, you will require a simple adapter cable. collapse

Black Box Explains...Solid vs. stranded cable.

Solid-conductor cable is designed for backbone and horizontal cable runs. Use it for runs between two wiring closets or from the wiring closet to a wallplate. Solid cable shouldn’t be... more/see it nowbent, flexed, or twisted repeatedly. Its attenuation is lower than that of stranded-conductor cable.

Stranded cable is for use in shorter runs between network interface cards (NICs) and wallplates or between concentrators and patch panels, hubs, and other rackmounted equipment. Stranded-conductor cable is much more flexible than solid-core cable. However, attenuation is higher in stranded-conductor cable, so the total length of stranded cable in your system should be kept to a minimum to reduce signal degradation. collapse

Black Box Explains...V.35, the Faster Serial Interface.

V.35 is the ITU (formerly CCITT) standard termed “Data Transmission at 48 kbps Using 60–108 KHz Group-Band Circuits.“

Basically, V.35 is a high-speed serial interface designed to support both higher data... more/see it nowrates and connectivity between DTEs (data-terminal equipment) or DCEs (data-communication equipment) over digital lines.

Recognizable by its blocky, 34-pin connector, V.35 combines the bandwidth of several telephone circuits to provide the high-speed interface between a DTE or DCE and a CSU/DSU (Channel Service Unit/Data Service Unit).

Although it’s commonly used to support speeds ranging anywhere from 48 to 64 kbps, much higher rates are possible. For instance, maximum V.35 cable distances can theoretically range up to 4000 feet (1200 m) at speeds up to 100 kbps. Actual distances will depend on your equipment and cable.

To achieve such high speeds and great distances, V.35 combines both balanced and unbalanced voltage signals on the same interface. collapse

Black Box Explains...SCSI Ultra2 and LVD (Low-Voltage Differential).

Small Computer Systems Interface (SCSI), pronounced “scuzzy,” has been the dominant technology used to connect computers and high-speed peripherals since the 1980s. SCSI technology is constantly evolving to accommodate increased... more/see it nowbandwidth needs. One of the more recent developments is Ultra2 SCSI.

Because Ultra2 SCSI is backward compatible, it works with all legacy equipment. Ultra2 doubles the possible bandwidth on the bus from 40 to 80 MBps! Just as importantly, Ultra2 supports distances up to 12 meters (39.3 ft.) for a multiple-device configuration. Ultra2 uses Low-voltage Differential (LVD) techniques to transfer data at faster rates with fewer errors. Don’t confuse Ultra2 with LVD. Ultra2 is a data-transfer method; LVD is the signaling technique used to transfer the data.

Cables are very important when designing or upgrading a system to take advantage of Ultra2 SCSI. Cables and connectors must be of high quality and they should come from a reputable manufacturer to prevent crosstalk and minimize signal radiation. BLACK BOX® Ultra2 LVD cables are constructed of the finest-quality components to provide your system with the maximum protection and highest possible data-transfer rates. collapse

Black Box Explains...IEEE 1284

Introduced in 1994, the IEEE 1284 standard addresses data-transfer speeds and distance for parallel interfaces. Standard parallel interfaces support speeds of up to 150 kbps at distances of up to... more/see it now6 feet (1.8 m); IEEE 1284 parallel interfaces can send your data over 100 times faster at up to five times the distance!

Although the Centronics® interface enabled only unidirectional computer-to-peripheral data flow, the IEEE 1284 interface enables bidirectional flow so peripherals can send data to the computer.

The IEEE 1284 standard covers five separate parallel modes, from the original Centronics (with which it’s compatible) to the high-performance Enhanced Parallel Port (EPP) mode. The computer negotiates with the attached device to determine which mode to use. collapse

Black Box Explains...SCSI-1, SCSI-2, SCSI-3, and SCSI-5.

There are standards…and there are standards applied in real-world applications. This Black Box Explains illustrates how SCSI is interpreted by many SCSI manufacturers. Think of these as common SCSI connector... more/see it nowtypes, not as firm SCSI specifications. Notice, for instance, there’s a SCSI-5, which isn’t listed among the other approved and proposed specifications. However, for advanced SCSI multiport applications, SCSI-5 is often the connector of choice.

Supports transfer rates up to 5 MBps and seven SCSI devices on an 8-bit bus. The most common connector is the Centronics® 50 or a DB50. A Micro Ribbon 50 is also used for internal connections. SCSI-1 equipment, such as controllers, can also have Burndy 60 or 68 connectors.

SCSI-2 introduced optional 16- and 32-bit buses called “Wide SCSI.“ Transfer rate is normally 10 MBps but SCSI-2 can go up to 40 MBps with Wide and Fast SCSI. SCSI-2 usually features a Micro D 50-pin connector with thumbclips. It’s also known as Mini 50 or Micro DB50. A Micro Ribbon 60 connector may also be used for internal connections.

Found in many high-end systems, SCSI-3 commonly uses a Micro D 68-pin connector with thumbscrews. It’s also known as Mini 68. The most common bus width is 16 bits with transfer rates of 20 MBps.

SCSI-5 is also called a Very High-Density Connector Interface (VHDCI) or 0.8-mm connector. It’s similar to the SCSI-3 MD68 connector in that it has 68 pins, but it has a much smaller footprint. SCSI-5 is designed for SCSI-5, next-generation SCSI connections. Manufacturers are integrating this 0.8-mm design into controller cards. It’s also the connector of choice for advanced SCSI multiport applications. Up to four channels can be accommodated in one card slot. Connections are easier where space is limited. collapse

Black Box Explains...Serial ATA technology.

Introduced in the mid 1980s, the Advanced Technology Attachment (ATA) interconnect soon became the industry-standard parallel input/output bus interface for connecting internal storage devices. Ultra ATA, which builds on the... more/see it noworiginal parallel ATA interface, has become the most commonly used type of interconnect.

But in recent years, sharing digital video and audio files over high-speed networks and other data-intensive uses has placed greater demands on hard drives, optical drives, and media-storage peripherals. So, not surprisingly, Ultra ATA now faces competition from a new technology—Serial ATA.

As the name implies, this new interconnect uses a serial bus architecture instead of a parallel one. Serial ATA currently supports speeds up to 150 MBps. Further enhancements could to boost rates as high as 600 MBps.

Compared with Ultra ATA, Serial ATA offers distinct advantages, including a point-to-point topology that enables you to dedicate 150 MBps to each connected device. Each channel can work independently and, unlike the “master-slave” shared bus of Ultra ATA, there’s no drive contention or interface bandwidth sharing.

Compared with Ultra ATA’s parallel bus design, Serial ATA requires a single signal path for sending data bits and a second path for receiving acknowledgement data. Each path travels across a 2-wire differential pair, and the bus contains four signal lines per channel. Fewer interface signals means the interconnect cable requires less board space.

Serial ATA also uses thinner cables (no more than 0.25" wide) that are available in longer lengths (up to 1 meter) as well as an improved connector design to reduce crosstalk. It also offers hot-swappable capabilities.

Although Serial ATA can’t interface directly with earlier Ultra ATA devices, it complies fully with the ATA protocol, so software between the two interconnects is compatible. collapse

Black Box Explains...Choosing SCSI cables.

1. Quality. Your system’s performance depends on the quality of your SCSI cables. Without high-quality cables specifically designed for SCSI applications, you could be jeopardizing your SCSI lifeline. Inferior cables,... more/see it nowadapters, and terminators can cause random errors, data corruption, or even a system crash! Black Box® SCSI Cables and components are the absolute best-quality products. And they’re guaranteed for life.

2. Length. For peak network performance, make sure your cables are the right length. As cable runs get longer, signals weaken and are more susceptible to noise. Always use the shortest cable for the task. And stay within the SCSI-1 and SCSI-2 standards of six meters or three meters for Fast SCSI. Remember, this is the total length of the bus, including all internal and external cables. collapse

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