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Old 09-05-2006, 11:37 PM   #1 (permalink)
Imperial Space Womble
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Question Making Sence Of IBM Scsi Hard Drives IDs

I am currently putting together a computer with 2x IBM 9Gb SCSI Hard drives.

I have located the pin to set the SCSI ID, but I am still trying to work out how IBM comes up with these SCSI ID Numbers.

The pins are follows
1 ID Bit 3
2 ID Bit 2
3 ID Bit 1
4 ID Bit 0
5 Enanble Auto Spin
6 S/E Mode
7 Disable Unit ATTN
8 IT Sync Nego
9 Auto Start Delay
10 Delay Star 6 / 12
11 Disable Parity
12 Led Out

Jumpers on 5 only = SCSI ID 0
Jumpers on 5 and 4 (BIT 0) = SCSI ID 1
Jumpers on 5 and 3 (BIT 1) = SCSI ID 2
Jumpers on 5 and 2 (BIT 2)= SCSI ID 4
Jumpers on 5 and 1 (BIT 4)= Does not detect
Jumpers on 2 and 3 (BIT 2 & 3)= SCSI ID 6

Now normally I am used to the Seagate Drives where you add up the bits.
However this older IBM Drive seems to be defying that rule.

Some my question is this. What algorithm does IBM SCSI Hard Drives use to work out SCSI IDs?

Also, can some one explain to me the
* S/E Mode
* Disable Unit ATTN
* IT Sync Nego
* Auto Start Delay
* Delay Star 6 / 12
* Disable Parity
* Led Out


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Old 09-06-2006, 10:18 AM   #2 (permalink)
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gahhhh. peculiar. don't suppose it's binary :/

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Old 09-06-2006, 03:18 PM   #3 (permalink)
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Yes, it is like
off,off,off off (0000) = ID0
off,off,off,on(0001)= ID1
and so on:
ID bit 3 is for 68-pin hdd's only (at least for very old drives that i have)

BTW, auto-delay is very practical feature.
I had at some time 6 SCSI drives on one pc, and w/o delay all drives tried to start up immediately after power ON - as a result PSU overloaded and switched off after 1 second. After i put different delay for each hdd - all worked fine:-)
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Old 09-06-2006, 03:43 PM   #4 (permalink)
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