Change to SCSI Flex Disk Pin 2 Definition
Charles Monia 237-6757
monia at AM.SHRMSG.SHR.mts.dec.com
Fri Jan 31 07:09:11 PST 1997
* From the SCSI Reflector (scsi at symbios.com), posted by:
* Charles Monia 237-6757 <monia at AM.SHRMSG.SHR.mts.dec.com>
*
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From: Charles Monia
to: X3T10 Committee,
Gene Milligan
SBC Technical Editor
Subject: Proposed resolution of SCSI Flexible Disk Mode Page Issues
As Gene points out in the the attached note, the definition for SCSI 2 Flexible
Disk mode page PIN 2 is missing. In response to his reguest for input we
propose the resolutions discussed below. In addition, we comment on a couple
of other minor differences between SCSI -2, rev 10t and SBC.
Mode page disposition:
One of the alternative resolutions Gene suggests is to obsolete the page. Since
Digital currently supplies these drives in a number of systems, we request that
the page not be made obsolete.
Instead, we propose that following resolution for the PIN 2 mode page
discrepancy Gene identified. In the descriptions, SBC text references are to
revision 7. SCSI -2 references are from version 10t of X3.131.
Problem:
The contents of the PIN 2 field (see SBC table 76) are not defined.
Proposed resolution:
Digital agrees with Gene's alternative (c), that the field definition be made
vendor specific.
Rationale:
As Gene notes, the Pin 2 field has never been specified in the SCSI -2
standard. Since our experience indicates that this field has been implemented
in a vendor specific manner, we believe such a definition is appropriate at
this time.
PIN 4 Editorial Issue:
In SCSI -2, rev 10t, the PIN 4 definition (table 161) had the duplicate value
entries shown below:
SCSI-2 Definition (table 161):
Bit 7 6 5 4 Description of pin 4 use
----------- ------------------------
P 0 0 0 Open
P 0 0 1 Inuse
P 0 1 0 Eject
P 0 0 0 Head load
In SBC (table 79), this was changed to:
Bit 7 6 5 4 Description of pin 4 use
----------- ------------------------
P 0 0 0 Open
P 0 0 1 In use
P 0 1 0 Eject
P 1 0 0 Head load
Comment:
We concur with the change specified in SBC.
SCSI -2 Editorial Observation:
The SCSI-2 table defining the PIN 1 field (table 162) was mislabeled as the PIN
34 field. The error is corrected in SBC revision 7.
************************************************************ ***** *
* Charles Monia, Storage Architecture Group *
* Digital Equipment Co. Internet: charles.monia at shr.mts.dec.com *
* Tel: (508) 841-6757 X400: c=US; a=MCI; o=Digital; ou=SHR *
* Fax: (508) 841-6100 *
************************************************************ ***** *
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From: "Gene_Milligan at notes.seagate.com"
<"\"Gene_Milligan at notes.seagate.com\""@RAZZLD.STARCH.MRGATE.SHRMSG.SHR.mts.dec.com>
Subject: Change to SCSI Flex Disk Pin 2 Definition
To: monia at am.SHRMSG.SHR.mts.dec.com
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* From the SCSI Reflector (scsi at symbios.com), posted by:
* Gene Milligan <Gene_Milligan at notes.seagate.com>
*
The flexible disk page parameters for control and reporting of flexible disk
device parameters in SCSI-2 and SBC failed to define Pin 2.
X3T10 has authorized Digital, which was the only company to respond the prior
call for flexible disk page parameters for control information, to provide a
decision on which of the three alternatives below to address the remaining
deficiency in the FDD page parameters:
a) Make the page obsolete.
b) The FDD I/O standard X3.80 contains the following definition for Pin 2.
8-Inch Cartridge Drive Signals: HEAD CURRENT SWITCH / ACTIVE READ FILTER
5.25-Inch Cartridge Drive Signals: ACTIVE READ FILTER
HEAD CURRENT SWITCH / ACTIVE READ FILTER. (To the drive; head current
switch, mandatory, 8-inch only; active read filter, optional, 8-inch and
5.25-inch.) This interface signal is used for two different function, depending
on whether the drive is in the write or read mode. This signal should be in a
stable condition before attempting to read or write.
HEAD CURRENT SWITCH - Write Mode. The signal used as head current switch is
mandatory on 8-inch drives only. When this interface signal is true (low) and
the disk drive is selected, the lower value of the write current is selected
for a write operation on tracks 43 (decimal) through 76 (decimal). When this
interface signal is false (high) and the disk drive is selected, the higher
value of the write current is selected for a write operation on tracks 0
(decimal) through 42 (decimal).
ACTIVE READ FILTER - Read Mode. The signal used as active read filter is
optional on 8-inch and 5.25-inch drives. When this interface signal is true
(low) active and the disk drive is selected in a read operation, the read
signal is passed through an active filter network to form composite read data
on tracks 60 (decimal) through 76 (decimal). When this interface signal is
false (high) inactive and the disk drive is selected in a read operation, the
read signal is passed directly to form composite read data. The use of this
signal eliminates the need for write precompensation. When reading a flexible
disk cartridge that has been recorded using write precompensation, this signal
should remain in the false (high) inactive state.
Neither X3.80 nor its international version 9315 has ever been revised to
show the specifics of the 3.5-inch application.
SCSI-2 and SBC have a four bit Pin 2 field without any further definition of
its usage. Based upon the other pin definitions one of the bits would be
polarity. However there is no clue as to what the other values should be.
c) The Pin 2 field definition and field value will be made vendor specific.
If you have a definitive input to assist the decision, please state the input
in a response to the SCSI reflector by 1/27/97. Charles Monia of Digital will
forward the decision to the technical editor of SBC by 1/31/97.
Gene Milligan
SBC Technical Editor
*
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