SJ 20631-1997 Information Technology Small Computer System Interface - 2

This standard defines the input/output bus for interconnecting computers and peripheral devices. This standard defines an extension of the Small Computer System Interface (GB/T15533, referred to here as SCSI-1), and also provides a more complete standardization of the previously specified command set. In order to allow for interoperability between consistent devices, this standard includes the necessary provisions for the mechanical, electrical and functional characteristics of the interface. This standard is referred to here as SCSI-2, and the term SCSI is used where no distinction is needed between the two versions. SJ 20631-1997 Information Technology Small Computer System Interface-2 SJ20631-1997 Standard Download Decompression Password: www.bzxz.net

Military Standard of the Electronic Industry of the People's Republic of China FL7010
Information Technology
SJ 20631-97
Small Computer System Interface-2
Published on June 17, 1997bzxZ.net
Implemented on October 1, 1997
Approved by the Ministry of Electronics Industry of the People's Republic of China Foreword
Small Computer System Interface (SCSI) technology and its application have developed rapidly from the 1980s to the 1990s. From SCSI-1 to SCSI-2, there are corresponding international standards, namely ISO9316:1989 and ISO/IEC9316:1995. At present, SCSI-1 has a national standard, namely GB/T155331995, which is equivalent to ISO9316:1989. This standard is equivalent to the international standard ISO/IEC9316:1995 "Information Technology-Small Computer System Interface-2). Its technical performance is completely in line with the provisions of the international standard. It supports FastSCSI and WideSCSI, and the synchronous data transfer rate can reach 40MB/S. It supports command queuing and disconnection and reconnection operations. The interface protocol includes providing connections for multiple boot devices and multiple target devices, which allows parallel 1/O operations and greatly enhances the I/O capabilities of the system. The public command set and the special command set that allows the connection of various types of devices, as well as the message protocol for interface management and control make SCSI a highly intelligent parallel I/O bus.
This standard specifies the physical and logical characteristics of SCSI~2, as well as the public command set and device-specific command set for disks, optical disks, tapes, printers, processors, CD-ROMs, scanners, media exchange devices and communication devices. While maintaining a high degree of compatibility with SCSI-1, this standard expands and enhances the functions of SCST-1. YKAoNKAca
Internationally, ISO/IEC9316:1995 has been technically revised to replace [S09316:1989 "Information Processing System Small Computer System Interface (SCSI)". In my country, this standard adopts the international standard ISO/IEC9316:199S "Information Technology Small Computer System Interface ~2): GR/T15533-1995 (Information Processing System Small Computer Interface) is equivalent to the international standard ISSO9316:1989. This standard includes the following parts: Chapter 1 Scope
Chapter 2 References
Chapter 3 Definitions, Symbols and Abbreviations
Chapter 4 General
Chapter 5 Physical Characteristics
Chapter 6 Logical Characteristics
Chapter 7 SCSI Commands and Status
Chapter 8.3
All Device Types
Chapter 9
Direct Access Devices
Chapter 10
Chapter 11
Sequential Access Devices
Printer Devices
Chapter 12
Processor Devices
Chapter 13
Chapter 14
Write Once Devices
CD-ROM Equipment
Chapter 15
Scanner Equipment
Chapter 16
Optical Storage Equipment
Chapter 17 Media Switching Equipment
Chapter 18 Communication Equipment
SCS[Signal Timing Examples (Reference)
Appendix A
Appendix B Fast SCSI Time Difference Timing (Reference) Appendix C Other SCSI Standardization Activities (Reference) Appendix ID Number Order (Reference)
Appendix E Vendor Identification (Reference)
SCSI protocol design provides an effective peer-to-peer 1/0 bus with 16 devices, including one or more hosts. Data can be transferred asynchronously, and the rate is only related to the implementation equipment and cable length. It supports synchronous data transfer at a rate of up to 10 megabytes per second. When 32-bit wide data transfer is selected, the data rate can reach 40 megabytes per second. SCSI-2 includes disks, optical
In 1985, when the first SCSI international standard was being finalized, some manufacturers wanted to add some of the requirements necessary for SCSI and further define the features of direct access devices. Rather than delay the SCSI standard, an ad hoc group was formed to develop a working document that was eventually called the Common Command Set (CCS), and many disk products have been designed using this working document.
While the CCS working document was being developed, work began on an enhanced SCSI standard called SCSI-2. SCSI-2 incorporated the results of the CCS working document and extended it to all device types. Cache commands were added, enhanced features were implemented, and other valuable functionality was added. Although SCSI-2 surpassed the original standard (now called SCSI-1), SCSI-2 remains highly compatible with SCSI-1. There has been a significant development from SCSI-1 to SCSI-2, with about three times more new data. The most significant change is the addition, but some unnecessary options have also been cancelled: a) Single boot device option; b) Non-arbitration system option; c) SCSI-11 type shielded connector; d) Non-extended asserted data option: e) Reservation queue option; f) Read-only device command set. There are some new low-level requirements: a) Require odd parity; b) Require the boot device to provide terminator power; ) Arbitration delay increased from 2.2S to 2.4uS; d) Require message support.
Added some low-level options
a) Wide SCSI (up to 32 bits wide using a second cable);
fast SCSI (synchronous data transfer up to 10 megabits per second);
command queuing (up to 256 commands per logical unit per boot device);
d) added high-density connector options;
e) asynchronous event notification;
f) occasional connections for extended boot.
New command sets added include:
a) CD-R(M) (replace read-only devices);
b) scanner devices;
c) optical storage devices (provided for write-once, read-only and erasable media);
d) media exchange devices;
e) communications devices.
The entire command set has been enhanced:
a) Device models have been added;
b) Extension assertion has been extended;
c) Number of inquiries has been extended;
d) Mode selection and mode assertion command paging has been added to all device types:
e) Replace definition, record selection, record assertion, read buffer and write buffer commands have been added to all device types! f) Copy command definition has been extended to include inaccurate block length handling and image copy selection;
The direct access device command set has been enhanced to add cache management, some new commands and provide TTTKAONTKAca-
More boot device control for defect management:
h) The sequential access device command set has been enhanced to add the concept of partitioned media:
i) The printer device command set has been enhanced by adding several mode pages:
i) The write once (optical) device command set has been enhanced by adding several new commands, plus several command blocks have been extended to 12 bytes to accommodate larger transfer lengths. 1 Scope
People's Republic of China Electronic Industry Military Standard Information Technology
Small Computer System Interface-2
Inforimnation Technology - Srmall ComputerSystem Interface-2
SJ 20631-97
This standard defines the input/output bus for interconnecting computers and peripheral devices. This standard defines the small computer system interface (GB/T15533,This standard is an extension of SCSI-1, referred to herein as SCSI-2, and provides a more complete standardization of previously specified command sets. In order to allow interoperability between conforming devices, this standard includes the necessary provisions for the mechanical, electrical, and functional characteristics of the interface. This standard is referred to herein as SCSI-2, and the term SCSI is used where no distinction is required between the two versions.
2 Referenced Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. The versions shown are valid at the time of publication of this standard. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards.
GB 1988 - 89
GB/T 15533 - 199S
GB6107-85
ISO/IEC 8482:1993
ISO/IEC 10149:1989
ISSO/IEC 10222: - 1)
IEC 908:1987
ISO) DIS 9324
ISO9318-2:1990
ISQO 9318 - 3: 1990
3Definitions, symbols and abbreviations
3.1 Definitions
Information processingSeven-bit coded character set for information interchangeInformation processing systemsSmall computer system interfaceInterface between data terminal equipment and data circuit-terminating equipment using serial binary data interchange
Information technologyTelecommunications and information exchange between twisted pair multipoint connection systemsInformation technologyData exchange on 120 mm CD-ROMs
Information processing systemsEnhanced small equipment interfaceCD digital audio system
Memory module interface
Intelligent peripheral device interface-2
Intelligent peripheral device interface-3
In this standard, the following definitions apply
1) To be published
The Ministry of Electronics Industry of the People's Republic of ChinaIssued on June 17, 1997 and implemented on October 1, 1997
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3. 1. 1 Active I/0 processactive 1/0 Process is the I/O process currently being executed (no queue). 3.1.2 Byte byte
represents an 8-bit structure.
3.1.3 Command description block CommandDescriptorBlock (CDB) This structure is used to transmit commands from the initiator to the target device. 3.1.4 Command queue cmmand queue
A queue used to store queued I/O processes (see 7.8). 3.1.5 Connection connect
The function of the initiator device to select the target device in order to establish a connection and start an I/O process. The connection result is an initial connection method.
3.1.6 Connection method connection
An initial connection method or a new connection method. This connection method only appears between an initiator device and a target device. 3.1.7 Contact contact
The conductive part of the connector associated with a single conductor in a cable. 3.1.8 contingent allegiance A unique condition generated by the check condition state during which the target device holds asserted data (see 7.6). 3.1.9 current I/0 process currentI/0process The I/0 process currently connected to the SCSI bus. 3.1.10 disconnect
The action that occurs when the SSCSI device releases control of the SSCSI bus, allowing the bus to enter the idle phase. 3.1.11 extended contingent allegiance In a multi-boot device system, a condition generated by the boot recovery message to speed up the extended error recovery process (see 7.7)
3.1.12 field
= a combination of one or more contiguous bits.
3.1.13 host adapter hostadapter
The device that connects the host system to the SCSI bus. The device usually implements the SCSI low-level protocol and normally operates in the role of an initiator. This functionality can be integrated into the host system. 3.1.14 Initial connection method The initial connection method is the result of a connection. The initial connection exists from the establishment of the BSY signal in the selection phase until the next bus idle phase occurs.
3.1.15 Initiator
A SCSI device that requests another SCSI device (standard device) to complete a certain I/O process. 3.1.16 Invalid
An illegal (reserved) or unsupported field or code value. 3.1.17/0 process
A 1/0 process consists of an initial connection and zero or more reconnections, all belonging to a single or a group of connection commands. More precisely, this connection method belongs to the connection in the transmission of zero or more command description blocks. With the establishment of a connection, an 1/0 process begins. Usually an I/O process ends in the bus idle phase after successfully transmitting a command completion message or releasing an embedded reset message. The I/O process also ends in the bus idle phase after an abort, abort tag, bus device reset, clear queued message or hard reset condition, or an unexpected disconnect occurs. 3.1.18 I--T connection I-T nexus exists between an initiator device and a target device. 3.1.19 I-T-L connection I-TL nexus exists between an initiator device, a target device and a logical unit. This relationship can replace the previous I-T connection.
3.1.20 IT--R connection I-T-R nexus exists between an initiator device, a target device and a target routine. This relationship can replace the previous I-T connection.
3.1.21 I—r--X connection ITX nexus is any of the connections JT—L or r—T—R. 3.1.22 I—T—L—Q I-T--LQ connection between an initiator, a target, a logical unit and a queue tag after the nexus successfully receives a queue tag message. This relationship can replace the previous [-T--L connection. 3. t.23 [—T—x—y connection IT--x--y nexus is any of the connections [—T—X or I—T—L—Q. 3.1.24 logicalblock logicalblock
a unit of data provided or requested by the initiator. 3.1.25 logicalunit logicalunit
a physical or virtual peripheral addressable by a target device. 3.1.26 logicalunitnumber logicalunitnumber a three-bit coded identifier for a logical unit. 3.1.27 mandatory
basic items required to conform to this standard
3.1.28 nexus
a relationship beginning with the establishment of the initial connection interface and ending with the completion of an I/O process, which may be qualified by the successful transfer of an identification message to specify a single logical component or target instance. The relationship may be further qualified by the successful transfer of an enqueue tag message.
3.1.29 one
a true signal value or a variable true condition.
3.1.30 optional
reference items are not required to conform to this standard, and the implementation of the optional items must be defined in this standard. 3.1.31 page
a general parameter structure used in some commands is called a page, and these pages are represented by values ​​called page numbers. 3.1.32 peripheral device a physical peripheral device that can be mounted on a SCSI device and connected to the SCSI bus. The peripheral devices and SCSI device peripheral controllers can actually be assembled together. Usually, there is a one-to-one correspondence between peripheral devices and logical components, but this is not required. Examples of peripheral devices are: disks, printers, CD-ROMs, and tapes. 3.1.33 Queue tag
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For the same room device, the queue tag is a value that can uniquely identify an I/0 process from other queued I/0 processes on the logical unit.
3.1.34 Queued I/0 process queuedI/0process is an I/0 process in the command queue. 3.1.35 Reconnect reconnect
The action of restoring a connection in order to continue an I/0 process. The target device reconnects to an initiator device by using the reselect phase and the message in phase after winning arbitration. The initiator device reconnects to a target device by using the select phase and the message out phase after winning arbitration. (See 7.5.2) 3.1.36 Reconnection reconnection is the result of reconnection. It exists from the establishment of the BSY signal in the select phase or reselect phase to the occurrence of the next bus empty phase. 3.1.37 reserved
Used to identify bits, fields, and code values ​​that are not currently being considered for future standardization. 3.1.38 SCSI address SCSIaddress
A unique address in hexadecimal notation (0-15) assigned to a SCSI device. This address is usually assigned and set in the SCS1 device during system installation.
3.1.39 SCSI ID
A bitwise representation of a SCSI address, referring to one of the signal lines DB (7-0). 3.1.40 SCSI device SCSIdevice
A host adapter or device controller that can be installed on an SCS bus. 3.1.41 signal assertion signal assertion The action of causing a signal to be driven to true.
3.1.42 Signal negation signal negation The action of driving a signal to a pseudo state, or allowing the cable terminator signal to be biased to a pseudo state (by putting the driver into a high impedance state).
3.1.43 Signal release signal release The action of allowing the cable terminator signal to be biased to a pseudo state (by putting the driver into a high impedance state). 3.1.44 Status status
A byte of information sent from the target device to the initiator device when each command is completed. 3.1.45 Target device target
The SCSI device that performs the operation requested by the initiator device. 3.1.46 Target routine target routine A target routine is an 1/0 procedure that points to the non-display logic of the target device (see 6.6.7). 3.1.47 third-party
When using the copy command, third-party means a copy command issued to one device to perform a copy operation between two other devices. When using the reserve or release command, third-party means that a reservation is made for another device (for example, for the exclusive use of sequential access devices, the processor device requests that the direct access device reserve itself). 3.1.48 unexpected disconnect A disconnect that occurs as a result of an abnormal situation (see 6.1.1). 3.1.49 vendor-specific (VS) 4—
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Something not specified by this standard (e.g., bits, fields, code values, etc.) may be used in various different implementations. 3.1.500 ero
False signal value or variable damage condition.
3.2 Symbols and abbreviations
SCSI-1
Asynchronous event notification (see 7.5.5)
American wire gauge
Least significant bit
Logical unit number
Most significant bit
A transfer from one device to another in SCSI-1 or SCSI-2
Small Computer System Interface (GB/T15533) Small Computer System Interface-2 (this standard) SCSI-2
4 General
4.1 Overview
SCSI is a device that can be used in multiple A local I/O bus that operates over a range of data rates. The primary purpose of the interface is to provide device independence to the host computer within a class of devices. Thus, a wide variety of disk drives, tape drives, printers, optical media drives, and other devices can be added to the host computer without modifying the general system hardware and software. Proprietary features and functions can be added through the use of vendor-specific fields and codes. Reserved fields and codes are provided for further standardization.
A second major purpose of SCSI-2 is to provide compatibility with SCSI-1 devices, support bus parity checking, and meet SCSI-1 Level 2 conformance. While vendor-specific commands and parameters are defined in advance by the SCSI-2 standard, SCSI-1 and SCSI-2 compliant devices can coexist on the same bus. In a mixed environment of SCSI-1 and SCSI-2 devices, it is expected that the operating system will provide support for both command sets in order to operate. Devices that strictly conform to SCSI-1, both initiators and targets, will respond in a manner that is likely to accept rejection of SCSI-2 protocol extensions. All SCSI-2 protocol extensions are designed to allow such rejections and allow SCSI-1 devices to continue to operate when the extensions are not needed. The third major purpose of SCSI-2 is to convey device-related information to SCSI-2 devices. The command set definition allows a high-level operating system to obtain all the required initialization information from the installed SCSI-2 devices. According to the formalized sequence of requirements, the installed SCSI-2 device type, device characteristics, and all variable parameters supported by the device are identified. Further requirements can determine the device's readiness for operation, the media types supported by the device, and all other appropriate system information. For operation, initialization, or system adjustment, those parameters that the operating system does not need are not affected by the SCSI-2 interface and are managed by the SCSI-2 device itself.
For all data blocks, the interface uses logical addressing rather than physical addressing. For direct access devices, each logical unit can be queried to determine how many data blocks it contains. A logical unit can correspond to all or some of the peripheral devices.
The interface protocol contains provisions for connecting multiple initiators (multiple SCSI devices with the ability to initiate operations) and multiple targets (multiple SCSI devices with the ability to respond to requests to perform operations). Distribution (i.e., bus conflict logic) is built into the SCSI architecture. In order to use the bus, the priority system awards interface control to the SCSI device with the highest priority in the competition. The time to complete arbitration is independent of the number of competing devices and can be completed in less than 10us. There are two electrical options: single-ended and differential. Single-ended devices and differential devices are electrically incompatible and cannot be mixed on the same physical bus. When using differential drivers and receivers, the maximum cable length provided can be up to 25m. When using single-ended drivers and receivers, the maximum cable length is specified to be 6m.It is mainly used in the chassis. Arbitration is defined to allow multiple boot devices and to allow parallel I/O operations. All SCSI devices are required to be able to operate under the asynchronous transfer protocol definition. In addition, an optional synchronous transfer protocol is defined. A message protocol is also specified for interface control. In most cases, the messages are not directly presented to the host computer software. Commands are divided into required, optional, or vendor-specific. SCSI devices are required to implement all required commands defined for the corresponding device type, and can also implement other commands. SCSI devices contain some commands that can simplify the writing of self-built driver software and can discover all necessary features without knowing the characteristics of specific peripheral devices (such as storage capacity) in advance. Although some commands implement a small logical block address space (221 blocks), many commands implement a large logical block address space (232 blocks).
Starting from Chapter 8 and each chapter of a dedicated device type, it consists of at least 4 items. The first is the device type model, which establishes the structure used to interpret the commands of this device type, discusses the properties and capabilities of the device type, and gives examples; the second defines the commands applicable to the device type; the third defines the parameters applicable to the device type, including diagnostic parameters, logging parameters, mode parameters, and important product data parameters that are sent as part of the corresponding command. Most parameters are formatted as pages; the fourth gives the definition of the terms specific to the device type. Each command in the chapters starting with Chapter 9 is unique to the device type or has an interpretation, field, or feature that is specific to the device type. For example, although the write command is used in multiple device types, the form is slightly different for each device type, and the parameters and meanings are also different. Therefore, each device type should be specified separately. 4.2 About
Certain words and terms used in this standard have special meanings beyond the general Chinese meaning. These words and terms are defined in Chapter 3 or in the text where they first appear. The Chinese names of signals, phases, messages, commands, states, assertion keys, additional assertion delay codes, and additional assertion code qualifiers are all underlined, and are represented in uppercase letters in English (e.g., REQUESTSENSE request assertion).
Fields containing only one bit are usually called name bits rather than name fields. Numbers not immediately followed by lowercase letters b or h are decimal values. Numbers immediately followed by lowercase letters b (××b) are binary values. Numbers immediately followed by lowercase letters h (××h) are hexadecimal values. 5 Physical Characteristics
This chapter contains the physical definition of SCSI-2, involving connectors, cables, signals, terminators, and bus timing values ​​necessary to implement the interface.
5.1 Physical Description
SCSI devices are daisy-chained, using a common 50-wire A cable, and optionally a 68-wire B cable! Both ends of each cable should be terminated. All signals are shared between all SCSI devices on the A cable. When wide SCSI is selected, wide SCSI devices need to be connected with an additional B cable. SCSI devices of various widths can be mixed.
Note 1: The method of selecting a 16-bit signal cable and the method of selecting a 32-bit signal cable are being defined, and the B cable definition will be cancelled in the future SCSI version.
Specifies two optional drivers/receivers: a) Single-ended driver and receiver, allowing a maximum cable length of 6m (mainly used for intra-machine connection): -6
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b) Differential driver and receiver, allowing a maximum cable length of 25m. On the same physical bus, single-ended and differential selections are usually mutually exclusive. Note 2. When fast synchronous data transmission is selected, it is not recommended to use single-ended drivers and receivers. 5.2 Cable requirements
The characteristic impedance of the cable should be not less than 90 and not greater than 1402. When implementing the fast synchronous data transmission option, the cable characteristic impedance used is defined in 5.2.3. NOTE 3 There have been successful single-ended implementations using cables with characteristic impedances less than 90 Ω. However, system integrity in single-ended implementations can be improved when the cable characteristic impedance is greater than 90 Ω. In addition to characteristic impedance, cable parameters are critical to system integrity and are under study as part of future SCSI documentation. To minimize noise effects, a minimum wire gauge of 0.08042 mm (28 AWG) should be used and, depending on proper distribution of termination power, smaller wire gauges may be used for signals other than terminator power. 4 To minimize discontinuities and signal reflections, cables with different impedances should not be used on the same bus. To achieve satisfactory system operation, trade-offs must be made between shielding effectiveness, cable length, number of loads, transfer rate, and cost. 5 To minimize discontinuities due to local impedance variations, a flat cable should be spaced a minimum of 1.27 mm (0.050 in) from other cables, other conductors, or itself when folded. 6 Adjustment mechanism can make larger gauge wires lubricated 5.2.1 Single-ended cable
A cable should use 50-wire flat cable or 25-signal twisted pair cable. If wide SCSI option is implemented, B cable should use 68-wire flat cable or 34-signal twisted pair cable. The maximum cumulative cable length should be 6m. If twisted pair cable is used, the twisted pair in the cable should be able to be connected to the actual docking point in the connector. The length allowed for the stub that is disconnected from the main line in any connected device or from any connection point shall not be greater than 0.1m.
Note 7: Avoid stubs in the case. The minimum distance between stubs should be 0.3m. SCSI bus termination should be at the end of each cable and can be inside the SCSI device at the end of the cable. 5.2.2 Differential impedance
A cable should use 50-wire flat cable or 25-signal twisted pair cable. If the Wide SCSI option is implemented, the B cable shall be 68-conductor flat cable or 34-signal twisted pair cable, with a maximum cumulative cable length of 25 m. If twisted pair cable is used, the twisted pairs in the cable shall be terminated at the actual mating point in the connector. No more than 0.2 m of stub length shall be allowed in any connected device or from any connection point that is disconnected from the main line.
SCSI bus termination loads shall be at the end of each cable and may be internal to the SCSI device at the end of the cable. NOTE 8: The use of twisted pair cable (twisted pair flat or twisted pair discrete) is strongly recommended. Without twisted pair, even at slow data rates and short distances, false pulses may result due to crosstalk between different signals and adjacent signals. 5.2.3 Cable Requirements for Rapid Isochronous Data Transfer In systems using the Rapid Isochronous Data Transfer option (see 5.8), the A cable and B cable shall meet the conductor size recommendations in 5.2. In shielded connectors, the cable shall have an overall shield suitable for termination. In such a system, the cable should have the following electrical characteristics: Characteristic impedance: 900 to 132n
Signal attenuation: 0.095dB per meter maximum at 5Mhz Pair-to-pair propagation delay: 0.20ns per meter maximum—7—
HKAONTKAcaThe B cable definition will be removed in future SCSI versions.
Specifies two alternative driver/receiver options: a) Single-ended driver and receiver, allowing a maximum cable length of 6m (primarily used for intra-machine connections): -6
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b) Differential driver and receiver, allowing a maximum cable length of 25m. Single-ended and differential options are usually mutually exclusive on the same physical bus. NOTE 2. Single-ended drivers and receivers are not recommended when the fast synchronous data transfer option is selected. 5.2 Cable Requirements
The characteristic impedance of the cable should be not less than 90Ω and not greater than 140Ω. When the fast synchronous data transfer option is implemented, the cable characteristic impedance used is defined in 5.2.3. NOTE 3: There have been successful implementations of single-ended using cables with characteristic impedances less than 90Ω. However, when the characteristic impedance of the cable is greater than 900Ω, the integrity of the system can be improved in single-ended implementations. In addition to characteristic impedance, cable parameters are critical to system integrity and are being studied as part of future SCSI documentation. To minimize noise effects, use the smallest wire possible, 0.08042 mm (28 AWG), and to ensure proper distribution of terminal power, smaller wire gauges may be used for signals other than terminator power. To minimize discontinuities and signal reflections, cables with different impedances should not be used on the same bus. To achieve full system operation, tradeoffs must be made between shielding effectiveness, cable length, number of loads, transmission rate, and cost. 5 To minimize discontinuities due to local impedance variations, fan-out cables should be spaced a minimum of 1.27 mm (0.050 in) from other cables, other conductors, or themselves when folded. 6 Adjustment mechanisms may allow larger wire gauges to be used. 5.2.1 Single-ended Cables
A cable should be 50-wire or 25-wire twisted pair. If the wide SCSI option is implemented, the B cable shall use 68-wire flat cable or 34-signal twisted pair cable, and the maximum cumulative cable length shall be 6m. If twisted pair cable is used, the twisted pair in the cable shall be connected to the actual mating point in the connector. The length allowed for stubs that are disconnected from the main line in any connected device or from any connection point shall not be greater than 0.1m.
Note 7: Avoid overlapping stubs, and the minimum distance between stubs shall be 0.3m. The SCSI bus termination shall be at the end of each cable and may be inside the SCSI device at the end of the cable. 5.2.2 Differential Susceptance
The A cable shall use 50-wire flat cable or 25-signal twisted pair cable. If the wide SCSI option is implemented, the B cable shall use 68-wire flat cable or 34-signal twisted pair cable, and the maximum cumulative cable length shall be 25m. If twisted pair cable is used, the twisted pair in the cable shall be connected to the actual mating point in the connector. The length of the stub that is allowed to be disconnected from the main line in any connected device or from any connection point shall not be greater than 0.2m.
SCSI bus termination loads shall be at the end of each cable and may be internal to the SCSI device at the end of the cable. NOTE 8: The use of twisted pair cable (twisted pair flat or twisted pair discrete) is strongly recommended. Without twisted pair, even at slow data rates and very short distances, false pulses may result due to the crosstalk between different signals and adjacent signals. 5.2.3 Cable requirements for rapid synchronous data transmission In systems using the rapid synchronous data transmission option (see 5.8), the A cable and B cable shall meet the conductor sizes recommended in 5.2. In shielded connectors, the cable shall have an integral shield suitable for termination. In such systems, the cable shall have the following electrical characteristics: Characteristic impedance: 900 to 132n
Signal attenuation: 0.095dB maximum per meter at 5MHz Pair-to-pair propagation delay: 0.20ns maximum per meter—7—
HKAONTKAcaThe B cable definition will be removed in future SCSI versions.
Specifies two alternative driver/receiver options: a) Single-ended driver and receiver, allowing a maximum cable length of 6m (primarily used for intra-machine connections): -6
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b) Differential driver and receiver, allowing a maximum cable length of 25m. Single-ended and differential options are usually mutually exclusive on the same physical bus. NOTE 2. Single-ended drivers and receivers are not recommended when the fast synchronous data transfer option is selected. 5.2 Cable Requirements
The characteristic impedance of the cable should be not less than 90Ω and not greater than 140Ω. When the fast synchronous data transfer option is implemented, the cable characteristic impedance used is defined in 5.2.3. NOTE 3: There have been successful implementations of single-ended using cables with characteristic impedances less than 90Ω. However, when the characteristic impedance of the cable is greater than 900Ω, the integrity of the system can be improved in single-ended implementations. In addition to characteristic impedance, cable parameters are critical to system integrity and are being studied as part of future SCSI documentation. To minimize noise effects, use the smallest wire possible, 0.08042 mm (28 AWG), and to ensure proper distribution of terminal power, smaller wire gauges may be used for signals other than terminator power. To minimize discontinuities and signal reflections, cables with different impedances should not be used on the same bus. To achieve full system operation, tradeoffs must be made between shielding effectiveness, cable length, number of loads, transmission rate, and cost. 5 To minimize discontinuities due to local impedance variations, fan-out cables should be spaced a minimum of 1.27 mm (0.050 in) from other cables, other conductors, or themselves when folded. 6 Adjustment mechanisms may allow larger wire gauges to be used. 5.2.1 Single-ended Cables
A cable should be 50-wire or 25-wire twisted pair. If the wide SCSI option is implemented, the B cable shall use 68-wire flat cable or 34-signal twisted pair cable, and the maximum cumulative cable length shall be 6m. If twisted pair cable is used, the twisted pair in the cable shall be connected to the actual mating point in the connector. The length allowed for stubs that are disconnected from the main line in any connected device or from any connection point shall not be greater than 0.1m.
Note 7: Avoid overlapping stubs, and the minimum distance between stubs shall be 0.3m. The SCSI bus termination shall be at the end of each cable and may be inside the SCSI device at the end of the cable. 5.2.2 Differential Susceptance
The A cable shall use 50-wire flat cable or 25-signal twisted pair cable. If the wide SCSI option is implemented, the B cable shall use 68-wire flat cable or 34-signal twisted pair cable, and the maximum cumulative cable length shall be 25m. If twisted pair cable is used, the twisted pair in the cable shall be connected to the actual mating point in the connector. The length of the stub that is allowed to be disconnected from the main line in any connected device or from any connection point shall not be greater than 0.2m.
SCSI bus termination loads shall be at the end of each cable and may be internal to the SCSI device at the end of the cable. NOTE 8: The use of twisted pair cable (twisted pair flat or twisted pair discrete) is strongly recommended. Without twisted pair, even at slow data rates and very short distances, false pulses may result due to the crosstalk between different signals and adjacent signals. 5.2.3 Cable requirements for rapid synchronous data transmission In systems using the rapid synchronous data transmission option (see 5.8), the A cable and B cable shall meet the conductor sizes recommended in 5.2. In shielded connectors, the cable shall have an integral shield suitable for termination. In such systems, the cable shall have the following electrical characteristics: Characteristic impedance: 900 to 132n
Signal attenuation: 0.095dB maximum per meter at 5MHz Pair-to-pair propagation delay: 0.20ns maximum per meter—7—
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