From ncrcom!enet-gw.pa.dec.com!subsys.enet.dec.com!ham Tue Aug 4 16:15 MDT 1992 Received: by ncr-mpd.FtCollins.NCR.COM; 4 Aug 92 16:15:32 MDT Received: from enet-gw.pa.dec.com by ncrcom.DaytonOH.NCR.COM id aa03480; 4 Aug 92 17:44 EDT Received: by enet-gw.pa.dec.com; id AA12676; Tue, 4 Aug 92 14:36:12 -0700 Message-Id: <9208042136.AA12676@enet-gw.pa.dec.com> Received: from subsys.enet; by decwrl.enet; Tue, 4 Aug 92 14:44:12 PDT Date: Tue, 4 Aug 92 14:44:12 PDT From: "Bill Ham DTN 237-2629, SHR3-2/W5" To: john.lohmeyer@FtCollinsCO.NCR.COM Cc: ham@subsys.enet.dec.com Apparently-To: john.lohmeyer@ftcollinsco.ncr.com Subject: SCSI HOT PLUGGING DRAFT Status: RO Gentlemen, Here is my attempt to send this SCSI hot plugging draft. Thanks for tweaking me on this as I have been somewhat derelict in getting you this electronic copy. Please advise if this copy is not adequate. Cheers, Bill TO: X3T9.2 SPI X3T9.2/92 - FROM: Bill Ham (DEC) SUBJECT: Hot Plugging Requirements for SPI DATE: May 19, 1992 PURPOSE: A section to be added to the SCSI-3 SPI document that allows hot plugging of devices is requested. Background information and some preliminary suggestions for wording are included. BACKGROUND: This document defines a set of conditions where hot plugging of devices is allowed. The SCSI bus is fully active during this entire process. Hot plugging of SCSI devices is being routinely done today by many users without problems. Some suppliers even specify their devices to be hot pluggable. Further, detailed analysis of the electrical transients produced by the proper hot plugging procedure for ANSI compliant devices on an active SCSI bus has shown insufficient intensity to cause any detectable effect on the active devices on the bus. The only electrical effect worthy of discussion is a very small change in the timing skew caused by slight distortions in the rising or falling edge of bus transitions if the hot plugging disturbance intersects this part of the waveform (rare). This distortion could be a few nanoseconds in the worst case. The latest revised SPI skew/timing budget makes adequate allowance for this possibility. The hot plugging process must be executed properly to avoid causing problems. In extreme cases improper procedures can cause data damage and physical damage to other devices on the bus. Following are the requirements: PRELIMINARY WORDING FOR SCSI DEVICE HOT PLUGGING REQUIREMENTS: .All bus traffic into and out of the hot plugged device shall be stopped prior to its removal .The hot plugged device shall have bus drivers that conform to the requirements for glitch free power up/down in Sections 6.1.1 and 6.2.1 of this document .A device being added to the active bus shall make its power ground and logic ground connection at least 1 millisecond prior to the connection of any device connector pin to the bus -- these ground connections shall be maintained during and after the connection of the device to the bus .A device being removed from an active bus shall maintain its power ground and logic ground prior to, during, and for at least one millisecond after the disconnection of any device connector pin from the bus .The power to the electronics and mechanics of the device may be simultaneously switched with the bus pins IF the power distribution system is able to maintain adequate power stability to other devices during the transition AND the grounding requirements above are met NOTE: Some devices require moving the mechanics (HDA etc.) in order to connect or disconnect the power source or bus. In these cases the devices must be able to withstand the mechanical stresses imposed by the movement. For these devices it is recommended that the power (but not the grounds) be removed and that time be allowed for the device to reach a stable state prior to the movement of the device. .The device being added or removed from the bus shall not have more than 30 pF capacitance at the device connector in its unpowered state .Devices remaining on the active bus shall have SCSI-3 compliant receivers .The initialization of a newly installed device must be accomplished without disrupting other devices on the bus