To:         X3T9.2 Committee (SCSI)                        X3T9.2/92-133 Rev 8

From:       Scott Smyers (Apple Computer)

Subject:    Proposal to add a disconnect after command phase mode bit for
            SCSI-3

Date:       February 19, 1993

This is a SCSI-3 proposal that adds a new bit, called the Disconnect
Immediate bit (DImm), to the Disconnect-Reconnect mode page (mode page 2). 
The DImm bit controls the behavior of the target after a command phase.  If
the DImm bit is set to one, the target shall disconnect immediately after any
command phase, unless the DiscPriv bit in the latest IDENTIFY message is set
to zero.

This proposal also increases the size of the DTDC field in mode page 2 from
2 bits to 3 bits.  This proposal adds no new codings or functions to the DTDC
field other than those defined in SCSI-2.  In other words, the encoding of
the DTDC field remains as defined in SCSI-2 with the most significant bit set
to 0.

The table below and the text which follows it formally define the DImm bit. 
The table is taken from the SCSI-2 standard, rev 10h, section 7.3.3.2.

+=====-========-========-========-========-========-========-========-========+
|  Bit|   7    |   6    |   5    |   4    |   3    |   2    |   1    |   0    |
|Byte |        |        |        |        |        |        |        |        |
|=====+========+========+=====================================================|
| 0   |   PS   |Reserved|         Page Code (02h)                             |
|-----+-----------------------------------------------------------------------|
| 1   |                           Page Length (0Eh)                           |
|-----+-----------------------------------------------------------------------|
| 2   |                           Buffer Full Ratio                           |
|-----+-----------------------------------------------------------------------|
| 3   |                           Buffer Empty Ratio                          |
|-----+-----------------------------------------------------------------------|
| 4   | (MSB)                                                                 |
|-----+---                        Bus Inactivity Limit                     ---|
| 5   |                                                                 (LSB) |
|-----+-----------------------------------------------------------------------|
| 6   | (MSB)                                                                 |
|-----+---                        Disconnect Time Limit                    ---|
| 7   |                                                                 (LSB) |
|-----+-----------------------------------------------------------------------|
| 8   | (MSB)                                                                 |
|-----+---                        Connect Time Limit                       ---|
| 9   |                                                                 (LSB) |
|-----+-----------------------------------------------------------------------|
| 10  | (MSB)                                                                 |
|-----+---                        Maximum Burst Size                       ---|
| 11  |                                                                 (LSB) |
|-----+-----------------------------------------------------------------------|
| 12  |             Reserved              |  DImm  |           DTDC           |
|-----+-----------------------------------------------------------------------|
| 13  |                           Reserved                                    |
|-----+-----------------------------------------------------------------------|
| 14  |                           Reserved                                    |
|-----+-----------------------------------------------------------------------|
| 15  |                           Reserved                                    |
+=============================================================================+

A disconnect immediate (DImm) bit of zero indicates that the target may
disconnect after command phase if it chooses to do so based on its internal
algorithms, the setting of the DiscPriv bit in the IDENTIFY message and the
settings of the other parameters in this mode page.

A disconnect immediate (DImm) bit of one indicates that the target shall
attempt to disconnect immediately after every command phase for those
connections in which disconnections are allowed.