This is an excerpt from IBM's technical section.
http://www.storage.ibm.com/techsup/hddtech/dhas/dhaseis.htm
Pin Signal name Pin Signal name
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01 +5V 02 +5V
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03 RET 04 RET
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05 GND 06 DB0
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07 GND 08 DB1
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09 GND 10 DB2
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11 GND 12 DB3
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13 GND 14 DB4
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15 GND 16 DB5
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17 KEY 18 DB6
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19 GND 20 DB7
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21 GND 22 PARITY
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23 GND 24 TERM PWR
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25 -ATTN 26 -BSY
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27 GND 28 -ACK
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29 -RST 30 -MSG
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31 GND 32 -SEL
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33 -I/O 34 -C/D
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35 GND 36 -REQ
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37 RET 38 RET
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39 +5V 40 +5V
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The J2 pin assignments:
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Pin Signal name Pin Signal name
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1 (Unused) 2 -No Spin Up
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3 -INDEX 4 (Unused)
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5 -ID1 6 -ID2
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7 -ID4 8 -LED
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Note: If pin 2 is grounded the drive will not spin up at power on. The drive must be started with a start stop unit command.
Signal line descriptions
| BSY | BUSY indicates that the bus is in use | SEL | SELECT is used by an Initiator to select a Target or by a Target to re-select an Initiator | C/D | CONTROL DATA indicates whether control (1) or data (0) information is on the bus | I/O | INPUT/OUTPUT indicates whether the data on the bus is an input (1) to the Initiator or an output (0) to the Target. This line is also used to differentiate between SELECTION phase (0) and RE-SELECTION phase (1) | MSG | MESSAGE is driven by Target and indicates a message phase | REQ | REQUEST is driven by Target and indicates a request for a REQ/ACK data transfer handshake | ACK | ACKNOWLEDGE is driven by the Initiator and indicates an acknowledgement of a REQ/ACK data transfer handshake | ATN | ATTENTION is driven by an Initiator to inform a Target that the Initiator has a message ready | RST | RSET clears all SCSI devices from the bus and resets them Note: The target will not drive this line | DB(n) | 8 data bits are used to transfer data over the bus. DB(7) is the most significant | DB(P) | PARITY bit associated with DB(7-0). Data parity is odd | ID(n) | These signal pins are used to set the drive address | INDEX | The signal is just for reference, and the function is not specified | LED | The signal is just for reference, and the function is not specified |