simple SCSI question

emaney smsrks2007 at
Wed Jun 20 11:42:30 UTC 2007

Scott Long-2 wrote:
> emaney wrote:
>> iam a student and new to SCSI, i have a question please someone help me
>> to
>> get the answer for this
>> following question
>> how an ‘initiator’ on a SCSI bus identifies the logical entity with which
>> it
>> wants to communicate?
>> can anyone help me with this question, iam not getting whats is logical
>> entity
> A parallel SCSI initiator will do two steps to identify the "logical
> entity" that it wants to talk to.  First, it'll select the target by
> raising a signal on one of the 16 data lines.  Once the target has
> responded, the initiator will send a series of 1 or more message bytes
> that identify the LUN inside the target that the upcoming command is
> for.  This is a gross simplification of how the SCSI wire protocol
> works, and I suggest reading some of the docs on for more
> information.
> Scott
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somewhere else i read following about initiator identifying logical it similar to what you have said?
The SCSI ID of the target is selected in the selection phase (BSY & SEL 
asserted, Data lines that corresponds to initator ID and target ID 
asserted). The initiator should also assert ATN in the selection phase. 
The MESSAGE OUT phase (BSY & C/D & MSG asserted) forced by ATN can now 
be use by the initiator to send an IDENTIFY message to select the LUN. 

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