Adaptec PCM-3420, PC/104 manual Chronous

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F

FAST SCSI

Provides for performance and compatibility enhancements to SCSI-1 by increasing the maximum synchronous data transfer rate on the SCSI bus from 5 MBytes/sec to 10 MBytes/sec.

There are 2 handshaking modes on the SCSI bus, used for transferring data: ASYNCHRONOUS and SYNCHRONOUS. ASYNCHRONOUS is a classic Req/Ack handshake. SYNCHRO- NOUS is “sort of” Req/Ack, only it allows you to issue multiple Req’s before receiving Ack’s. What this means in practice is that SYNCHRONOUS transfers are approx 3 times faster than ASYN-

CHRONOUS.

SCSI-1 allowed asynchronous transfers at up to 1.5 Mbytes/Sec and synchronous transfers at up to 5.0 Mbytes/Sec.

SCSI-2 had some of the timing margins “shaved” in order that faster handshaking could occur. The result is that asynchronous transfers can run at up to 3.0 bytes/Sec and

synchronous transfers at up to 10.0 Mbytes/Sec. The term “FAST” is generally applied to a SCSI device which can do synchronous transfers at speeds in excess of 5.0 Mbytes/Sec. This term can only be applied to SCSI-2 devices since SCSI-1 didn’t have the timing margins that allow for FAST transfers. A 10 MHz transfer rate for SCSI came out of a joint effort with the IPI (Intelligent Peripheral Interface) committee in ASC X3T9.3. Fast SCSI achieves 10 Megabytes/second on the A-Cable and with wider data paths of 16- and 32-bits can rise to 20 Megabytes/ second and even 40 Megabytes/second. However, by the time the market starts demanding 40 Megabytes/second it is likely that the effort to serialize the physical interface for SCSI-3 will attract high- performance SCSI users to the Fiber Channel.

A word of caution. At this time the fast parameters cannot be met by the Single Ended electrical class, and is only suitable for Differential. One of the goals in SCSI-3 is to identify the improve- ments needed to achieve 10 MHz operation with Single Ended components.

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Contents PCM-3420 PC/104 Fast SCSI-2 Module Page Copyright Notice AcknowledgementsPacking Set Contents Appendix B Pin Assignments Appendix a Installing PC/104 ModulesAppendix C Glossary of Technical Terms39 General Information Product Highlights IntroductionFeatures Peripheral Device SupportTechnical Specifications SpecificationsPhysical and Environmental Specifications Board layout Page Hardware Installation Jumpers and Connectors Jumpers Label FunctionJP6 JP7 JP2 Locating Jumpers & Connectors Setting Jumpers Installing PCM-3420 Module PrecautionsFactory Default Settings Jumper Configuration Reference JP2SD0 SD1 SD2 DMA DC1 DC2 This jumper block provides six major PCM-3420 operation mode CC000h CFFFFh Scsi Hard Disk Drive Connector CN1 Page EZ-SCSI Quick Reference Quick Start Instructions System Requirements for Full Installa- tionWindows 95 or Windows NT Windows/Windows for Workgroups DOSScsi Device Troubleshooting Troubleshooting TipsWindows 95/Windows NT Troubleshooting General Information Page General Information Information for DOS/Windows 3.1x Users DOS and Windows 3.1x Device DriverDOS and Windows 3.1x Aspi Managers DOS Formatting UtilitiesLow-level Formatter scsifmt Formatter and Partitioner afdisk Removable Media Manager rmvtool Page Installing PC/104 Modules Installing PC/104 modules PC/104 Module Mounting Diagram Page Pin Assignments PC/104 Connectors J1 , J2 Pin SignalInternal SCSI-2 Connector CN Page Glossary of Technical Terms Adaptec EZ-SCSI Termpwr GND Synchronous Transfer Bios Devicedriver DOS Partition Chronous Full Scsi IRQ Narrow Scsi device as opposed to Wide Scsi device Port I/O Address Scsi Device Taggedqueuing Termination Page Appendix C Glossary of Terms