Delay before reading SCSI ID pins?

Gerry_Houlder at Gerry_Houlder at
Fri May 15 15:00:36 PDT 1998

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* Gerry_Houlder at
Do not assume that all disk drives will wait 500 Msec before reading SCSI
ID lines. This will vary between vendors and may even vary between
different models from the same vendor. I recommend using MATED 1 as you
described to hold off the drive. We have had this request from several
customers already and this idea worked best for all of them.

For our Seagate  SCA-2 Parallel SCSI drives:
After power-on the firmware waits until MATED1 goes low, then waits at
least another 250ms before reading the SCSI ID's. If MATED1 is high at
power-on, the firmware will wait (forever if need be) until MATED1 goes low
before doing reading the SCSI ID.

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* Gary Watson <gary at>
Can I assume that disk drives wait at least 500ms after
power up before reading the SCSI ID lines?  If not, will
holding the MATED 1 line high until my box is ready
stall it off for a little while?  (Talking SCA-2 here...)
Gary Watson                   Trimm Technologies, Ltd.
Engineering Manager           Nottingham England
gary at              +44 (0) 115 951 9951

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