SCSI Terminations Specifications

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General Specifications


	SCSI Standards		See tables at the end of this help file for definitions of several features of SCSI standards.
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	SCSI-1		SCSI-1, the original SCSI, was standardized by ANSI in 1986. Allows asynchronous data transfer rates of 1.5 MB/sec and synchronous transfer rates to a maximum of 5 MB/sec. It has an 8-bit SCSI port that uses Single-ended open-collector drivers. Uses a 50-pin connector. SCSI-1 is an obsolete standard after the development of SCSI-2.
	Wide SCSI		This term is generally applied to WIDE (16-bit) SCSI with FAST data transfer rate of up to 10 Mbps
	Fast SCSI		Standard defined in SCSI-2. Increases the maximum data rate from 5 Mbps for NARROW (8-bit) SCSI to 10 Mbps.
	Wide Fast SCSI		This term is generally applied to WIDE (16-bit) SCSI with FAST data transfer rate of up to 20 Mbps
	Ultra SCSI		This is also known as Fast-20. It doubles the FAST SCSI data rate to up to 20 Mbps for the 8-bit bus
	Wide Ultra SCSI		Defines a maximum transfer data rate up to 40 Mbps for the WIDE (16-bit) SCSI.
	SCSI-2		SCSI-2 has significant improvements over SCSI-1 including faster data transfer rates, better connectors, wider bus path, better reliability via synchronous negotiation and parity checking. SCSI-2 has a data transfer rate from 5 MB/sec to 10 Mb/sec. This speed change is called Fast SCSI-2. Also, SCSI-2 provides the option to double the bus from 8 bits to 16 bits. This change is known as Wide SCSI. By combining the Fast SCSI-2 with the Wide SCSI bus a maximum data rate of 20 MB/sec can be achieved.
	Ultra2 SCSI		This is also known as Fast-40. It doubles the Ultra SCSI data rate to up to 40 Mbps for the 8-bit bus.
	Wide Ultra2 SCSI		Defines a maximum data rate of 80 Mbps for the WIDE (16-bit) SCSI.
	SCSI-3		The SCSI-3 specification allows for faster transfer rate, more devices on a single chain (a maximum of 32), and also it incorporates serial connections in addition to the traditional parallel interconnect of SCSI-2. The serial interconnect of SCSI-3 incorporates three technologies: Serial Storage Architecture (SSA), Fibre Channel, and IEEE P1394. The serial transfer mode allows faster data rates, more devices per bus, simple connectors, and longer cables.
	Ultra3 SCSI (Ultra160)		This is also known as Fast-80 or Ultra-160. It doubles the Ultra2 SCSI data rate to up to 160 Mbps for the 16-bit bus.
	Ultra320 SCSI		Defines a maximum data rate of 320 Mbps for the WIDE (16-bit) SCSI.
	Ultra640 SCSI		Defines a maximum data rate of 640 Mbps for the WIDE (16-bit) SCSI.
	Fibre Channel		A high-speed serial protocol for channels and networks that uses links of twisted-pair, coaxial cable or fiber optic cable. SCSI can use the Fibre Channel Arbitrary Loop topology (FC-AL).
	Serial SCSI (Firewire)		A very fast bus standard that supports data transfer rates of up to 400 Mbps Apple, which originally developed the technology, uses the trademarked name FireWire. The standards are defined in IEEE-1394.
	Other		Other, not listed, standards.
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	SCSI Terminator Class
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	Internal		A passive terminator installed in some SCSI drives used before the advent of LVD. The terminators can be enabled or disabled by setting of jumpers or by inserting or removing it from a socket.
	External		This type of terminator is connected in series with the SCSI device. It is also known as "feed-through" terminator.
	Selectable		Can select between internal and external termination.
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	SCSI Terminator Type
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	Passive		It is the simplest and least reliable terminator. It uses simple resistor networks to terminate the bus. Used for single ended SCSI-1 short systems with few connected devices. It is driven by the term power line on the bus. The equivalent impedance i around 132 ohms. Because typical impedances of most cables is between 85 and 110 ohms, this type of terminator does not provide good impedance matching.
	Active		Generally used for single-ended SCSI-2 devices. It is compatible with passive terminators. This type of terminator consists of resistor networks driven by voltage regulators inside the terminator. The voltage regulator generates a termination voltage from the Term Power (the TERMPWR pin) and keeps the terminator impedance to stay at around 110 ohms. This value provides good impedance matching form the bus.
	Active Negation		In single-ended SCSI buses, asserting a signal requires to drive the signal voltage low. De-asserting (negation) the signal means to drive the signal high. In active negation terminators the signal is drive high by the terminator, allowing a faster bus speed.
	Differential Terminator (HVD)		Also called HVD terminator or High Voltage Differential Terminator is a type of terminator used in differential systems only. It consists of a 330/150/330 resistor network combination. These types of terminators are not compatible with single ended or LVD systems or devices.
	Low-Voltage Differential (LVD)		A special form of active termination defined in the SPI-2 (SCSI Parallel Interface 2) and SPI-3 (SCSI Parallel Interface 3) documents of the SCSI-3 specifications. This type of terminator allows faster speed for Ultra2 and Ultra3 SCSI.
	Multimode (LVD / SE)		Terminator used in LVD systems that use multimode transceivers. Depending on the voltage level that appears at the DIFFSENSE pin of the cable, the transceiver automatically chooses between LVD and single ended (SE) when the devices are powered up. Active terminators in this type of SCSI are able to respond to the DIFFSENSE line. If the DIFFSENSE voltage is < 0.7 V, the terminator will be in the single ended mode; if this voltage is between 0.9 V and 1.9 V the terminator will be in the LVD mode.
	Forced Perfect Terminator (FPT)		This is a single-ended termination method utilizing diodes clamps to compensate for the impedance mismatch between the SCSI cable and the device connected to the bus. The diode clamps force the termination to the correct voltage. This termination is not recognized by the SCSI specifications.
	High Byte Terminator		High byte is the upper data byte on a wide bus (bits 8 to 15). High byte termination is used when the SCSI bus terminates in multiple locations.
	Other		Active De-Assertion Regulated (ADR), Signal Line Increased Current Kicker (SLICK), Feed-through, and others not listed.
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	SCSI Connector Type:		Connector and cable type uses to connect the terminator to the SCSI device.
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	Ribbon IDC 50 (Internal)		50-pin Insulation Displacement Connector (IDC). It is used with ribbon cables for internal (non-insulating) SCSI cabling. In SCSI terminology it is known as: Nonshielded Alternative 2, A-cable.
	50-pin Centronics		50-pin version of the connector used for parallel printers. Specified in SCSI-1; still used for narrow SCSI. Known as: Shielded Alternative 1, A-cable.
	50-pin Micro-D		Smaller than the Centronics connector. Specified to have spring-latch fasteners. Male connector used for cables, female for devices. Known as: Alternative 1, A-cable (shielded or non-shielded).
	68-pin Micro-D		Specified in SCSI-3 to allow the use of one cable in wide (16-bit) applications. Male connector is used in cables, female in devices. Known as: Alternative 3, P-cable (shielded or non-shielded).
	68-pin VHDCI		Very High Density Interconnect (VHDCI). Specified in SCSI-3. Similar to Centronics, but on a smaller pitch (0.8 mm). Known as: Shielded Alternative 4, P-cable.
	80-pin SCA		Single Connector Adapter (SCA) was specified in SCSI-3 to connect devices on hot-swap backplanes. Known as: Non-shielded Alternative 4, P-cable.
	Other		DB-25, 30-pin HDI, 50-pin high density micro-D, 60-pin high-density, etc.
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	Mounting / Form Factor
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	Flanged		Terminators are flange-mounted.
	Board-level Unit		Board-level units are computer boards that are designed to be inserted in a carrier.
	Leaded		Terminators are mounted via one lead.
	Panel Mount		Panel-mounted devices have a threaded bushing which surrounds the shaft.
	Screw Terminals		Terminals are designed for screw mounting on a circuit board.
	Surface Mount (SMT / SMD)		Surface-mount technology (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top surface of the board. SMT devices (SMD) have a flat surface that is soldered to a flat pad on the face of the PCB. Typically, the PCB pad is coated with a paste-like formulation of solder and flux. With careful placement, SMT components on solder paste remain in position until elevated temperatures, usually from an infrared oven, melt the paste and solder the component leads to the PCB pads.
	Stand-alone Unit		Stand-alone units are independent units connected to a system.
	Through Hole		Through-hole technology (THT) mounts components on a printed circuit board (PCB) by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board.
	Other		Other, unlisted mounting types
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Features / Standards


	Features
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	LED Indicators		Devices use light emitting diodes (LEDs) to indicate conditions such as "power" or "busy".
	Heatsink		The terminator is mounted on a heatsink.
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	Standards and Certifications
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	RoHS Compliant		Restriction of Hazardous Substances (RoHS) is a European Union (EU) directive that requires all manufacturers of electronic and electrical equipment sold in Europe to demonstrate that their products contain only minimal levels of the following hazardous substances: lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl and polybrominated diphenyl ether. RoHS will become effective on July 1, 2006.
	ELV Directive		End-of-Life Vehicles (ELV) is a European Union (EU) directive that requires manufacturers of automotive products sold in Europe to demonstrate that their products contain only minimal levels of mercury, cadmium and lead. Lead can still be used as an alloying additive in copper, steel and aluminum.
	WEEE Compliant		Waste Electrical and Electronics Equipment (WEEE) is a European Union (EU) directive designed to encourage the reuse, recycling and recovery of electrical and electronic equipment. WEEE is also designed to improve the environmental impact and performance of this equipment. The WEEE directive establishes requirements and criteria for the collection, treatment, recycling and recovery of electrical and electronic equipment. It also makes producers responsible for financing these activities. Retailers and distributors must provide a way for consumers to return used or obsolete equipment without charge.
	CE / FCC Certified?		The unit conforms with the American requirements of the Federal Communication Commission (FCC) and with the European CE Marking (Conformite Europeene or European Conformity) system, which is helpful for exports to the countries of the European Economic Area (EEA).
	CSA		Products that bear a CSA Mark have been tested by the Canadian Standards Association (CSA) and meet applicable standards for safety and/or performance. These standards are written and administered by organizations such as the American National Standards Institute (ANSI), Underwriters Laboratories (UL), and CSA International. CSA Marks may appear alone or with indicators. CSA Marks that appear alone are used with products certified primarily for the Canadian market, to the applicable Canadian standards. CSA Marks that appear with the indicators “C” and “US” or “NRTL/C” are used with products certified for both the U.S. and Canadian markets, to the applicable U.S. and Canadian standards.
	IEC		The International Electrotechnical Commission (IEC) is a global, non-profit organization that develops and maintains voluntary quality, safety, and performance standards for electrical materials, products, and systems The IEC also publishes standards for the electronics and telecommunications industries. The IEC’s membership consists of the electrotechnical standards organizations from each of its 51 member nations. The American National Standards Institute (ANSI) represents the United States.
	UL		Underwriters Laboratories (UL) is a non-profit organization that tests components, systems, and materials according to its published standards for safety. Products that receive UL approval bear a UL Mark.
	Other		Other unlisted standards.
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