Basics of SCSI Fourth Edition - Manhattan Skyline GmbH

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Figure 15. Example of 68-pin “P" cables ("WIDE" bus) Note that the pinouts of the Single-Ended and HVD 68-pin connectors are different; this is similar to that of the Single-Ended and HVD 50-pin connectors. Note too, that the LVD 50-pin and 68-pin connectors use pinouts, shown on the next page, analogous to the Single-Ended versions. Basics of SCSI Fourth Edition 30
Figure 16. Example of LVD for NARROW and WIDE bus When designing a SCSI system, it is recommended that you use good quality cables from a reputable vendor. Always use cable with twisted pairs, whether the flat or the round type. NEVER use the non-twisted type for external cables; its sensitivity to electrical noise, and crosstalk often results in low signal quality and low electrical margin; that is not worth the small financial savings. SIGNAL CROSSTALK, NOISE IMMUNITY, AND SKEW IN SCSI CABLES To minimize radiation and crosstalk between signals in the cables, the following rules should be respected when building round SCSI cables: • Use a three-layer cable with three twisted-wire pairs in the core (inner layer), nine pairs in the middle layer (50-pin cables), and the remaining pairs in the outer layer, all enclosed by a shield and a PVC jacket. Thethreelayers should be capacitively separated from each other by twisting the pairs together in the opposite direction for each layer. The insulation used should be of the Polyolefin type (no PVC!!). • Place the two most critical pairs, the REQ and ACK, together with ground, in the core of the cable. Use the outside layer for the Data and Parity signals. Place the Control signals in the middle layer to insulate the REQ & ACK pairs from the Data pairs. Note that the Single-Ended and HVD connector pinouts are different, and therefore the optimal cable layout for each will be different. However, you may find that if you interchange the two, the Single-Ended cable will work on the HVD system most of the time (the HVD interface is more forgiving), but the HVD cable may not work on the Single-Ended system. Basics of SCSI Fourth Edition 31
Page 1 and 2: What is SCSI? Fourth Edition Basics
Page 3 and 4: Evolution of SCSI SCSI-1 SCSI-2 SCS
Page 5 and 6: existing computer with no hardware
Page 7 and 8: Figure 2. SCSI system with two Init
Page 9 and 10: WIDE & FAST & UltraSCSI The SCSI-1
Page 11 and 12: LOGICAL BLOCK ADDRESSING (LBA) Unif
Page 13 and 14: SCSI-3 redefined the device types a
Page 15 and 16: COMMAND LINKING The LINK and FLAG b
Page 17 and 18: In SCSI-1 it was allowed to skip th
Page 19 and 20: Initiator receives a Check Conditio
Page 21 and 22: Targets that implement the MODE SEL
Page 23 and 24: Basics of SCSI Fourth Edition 23
Page 25 and 26: SIGNAL DESCRIPTIONS BSY an "OR-tied
Page 27 and 28: The S-E and LVD devices can be conn
Page 29: CABLES AND CONNECTORS Several cable
Page 35 and 36: SCSI CABLE LENGTH & NUMBER OF DEVIC
Page 37 and 38: CONNECTING 8-BIT & 16-BIT DEVICES O
Page 41 and 42: smooth command execution. At the sa
Page 43 and 44: SCSI-2 Work on the new standard, SC
Page 45 and 46: Will SCSI-2 be replaced by SCSI-3 S
Page 47 and 48: SOURCES OF INFORMATION PUBLICATIONS
Page 49 and 50: SCSI Glossary ANSI American Nationa
Page 51 and 52: According to AT&T Bell Labs: data i
Page 53 and 54: 1,073,741,824 bytes. Broadly, one b
Page 55 and 56: ecorded after the last block. In or
Page 57 and 58: The circuitry that receives electri
Page 59: circuitry, a terminator can use sim

Basics of SCSI Fourth Edition - Manhattan Skyline GmbH

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