[This document only shows what changed since Rev 2] Date: Mar 9, 1990 X3T9.2/90-48 R4 To: X3T9.2 Committee (SCSI) From: George Penokie (IBM) Subject: 16/32 bit P/Q and L cable stand alone document Section 3 Issues -Redefine SCSI address and SCSI ID terms Section 4 Issues -Termination of the cable -The maximum number of devices should be made to be 16 if the P cable is used. -The maximum number of devices should be made to be 32 if the P/Q cable is used. -The maximum number of devices should be made to be 32 if the L cable is used. -Disallow B connector devices from connecting to P, P/Q, or L type devices. -Add in the Q cable changes. -Make the Q cable have the same pin positions for data lines as the P cable. This is to make dual porting easier. -Add in the L cable changes. -Make the L cable have the same pin positions for data and control lines as the P cable. This is to make dual porting easier. -Show examples of A cable to P cable, A cable to L cable, and P cable to L cable convertors. Section 5 Issues -Some wording changes in section 5.1.2 ARBITRATION Phase are required to indicate there are now 32 devices allowed on the bus. |-Add into section 5.1.3 SELECTION Phase wording to describe how to | handle parity detection on devices with more that 8 SCSI ID's -Some changes in section 5.1.5.3 Wide Data Transfer are required to indicate there is another cabling option. -Add in the Q cable changes -Add in the L cable changes -Added a table to show the legal combination of ACKQREQQ, Addr32, Addr16, Wbus32, and Wbus16 bits from the Inquiry Data Format table. Section 7 Issues -The copy commands segment Descriptor does not have room for a 5 bit source address and a 5 bit destination address. -Make a new set of Descriptors to handle a larger number of addresses. -Make a new ASC and ASCQ to handle unsupported SCSI addresses -Remove the new ASC and ASCQ. Unsupported SCSI addresses should be handled like any other parameter type error. -Add into the Inquiry data the 16/32 bit addressing information and the ACKB/REQB information. Section 8, 9, 10, 12, 13, 14, 15, and 16 Issues -The Release command and Reserve command do not have room for a 5 bit third party device ID -Make 10 byte commands for both the Release and Reserve commands Section 3 changes recommended to implement a single 68 pin connector Current Cables A Cable - 50 conductors. The SCSI-1/SCSI-2 8-bit cable. B Cable - 68 conductors. A second cable to expand the data path to 16 or 32 bits. Proposed Cables P Cable - 68 conductors. A 16-bit single-cable with the signals from the A cable on the center 50 pins. It is expected that one can mix A and P devices with an appropriate adapter. Q Cable - 68 conductors. This cable extends the P cable to 32 bits. The pin assignments are the same as for the P cable, but the control signals, except REQ and ACK, are not used. L Cable - 110 conductors. A 32-bit single-cable with the signals from the P cable on the center 68 pins. It is expected that one can mix A, P, and L devices with appropriate adapters. 5.1.3. SELECTION Phase The SELECTION phase allows an initiator to select a target for the purpose of initiating some target function (e.g., READ or WRITE command). During the SELECTION phase the I/O signal is negated so that this phase can be distinguished from the RESELECTION phase. The SCSI device that won the arbitration has both the BSY and SEL signals asserted and has delayed at least a bus clear delay plus a bus settle delay before ending the ARBITRATION phase. The SCSI device that won the arbitration becomes an initiator by not asserting the I/O signal. The initiator shall set the DATA BUS to a value which is the OR of its SCSI ID bit and the target's SCSI ID bit and it shall assert the ATN signal (indicating that a MESSAGE OUT phase is to follow the SELECTION phase). The initiator shall then wait at least two deskew delays and release the BSY signal. The initiator shall then wait at least a bus settle delay before looking for a response from the target. The target shall determine that it is selected when the SEL signal and its SCSI ID bit are true and the BSY and I/O signals are false for at least a bus settle delay. The selected target may examine the DATA BUS in order to determine the SCSI ID of the selecting initiator. The selected target shall then assert the BSY signal within a selection abort time of its most recent detection of being selected; this is required for correct operation of the selection time-out procedure. | The target shall use the protocol in the following list to determine |when parity shall be checked: | | (a)DB(P) shall always be checked for parity. | (b)DB(P1) shall only check for parity if there is at least one SCSI | ID bit active on bits DB(8) through DB(15). | (c)DB(P2) shall only check for parity if there is at least one SCSI | ID bit active on bits DB(16) through DB(23). | (d)DB(P3) shall only check for parity if there is at least one SCSI | ID bit active on bits DB(24) through DB(31). | | The target shall not respond to a selection if any one or more of the |following conditions occur: | | (a)No SCSI ID bits active on any of the DATA BUS bytes. | (b)Bad parity is detected | (c)More that two SCSI ID bits are on the DATA BUS | (d)No SCSI ID bits are on bits DB(0) through DB(7) and there are less | than two SCSI ID bits on the remaining bits of the DATA BUS. IMPLEMENTORS NOTE: If a target chooses to support the single initiator or selection without asserting ATN options of SCSI-1, it may respond as described in the SCSI-1 standard. No less than two deskew delays after the initiator detects the BSY signal is true, it shall release the SEL signal and may change the DATA BUS. The target shall wait until the SEL signal is false before asserting the REQ signal to enter an information transfer phase.