Synchronized Spindles Interface; Electrical Description - Seagate ST12400N Product Manual

Product Manual - Hawk 2 Family SCSI-2 (Volume 1), Rev. C
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10.2

Synchronized spindles interface

The Synchronized Spindles Interface (SSI) allows several drives operating from the same host to operate their
spindles at a synchronized rotational rate. Details of the electrical and physical interfaces follow in paragraphs
10.2.1 and 10.2.1.2 and 10.2.1.3. The system operation is described in paragraph 5.7.
10.2.1

Electrical description

The electrical interface consists of one digital TTL reference index signal and ground. The reference index signal
(REFIND+) is an output if the drive is configured as a master and is an input otherwise. The reference index
signal is connected from drive to drive in a daisy-chain fashion as shown in Figure 5.7-1.
10.2.1.1 Drivers and receivers
Figure 10.2.1-1 shows a diagram of the driver/receiver circuit. The driver circuits have the following electrical
specifications.
Negated (False): 0.0 V to +0.4 V @ I =
Asserted (True):+ 2.24 V to +5.25 V @ I = +250 uA.
Notes.
[1] This connection is found only on "NC" drive models.
[2] See paragraph 10.2.1.1
Figure 10.2.1-1. SCSI reference index signal driver/receiver combination
10.2.1.2 Termination
The reference index signal (REFIND+) is terminated with a 2.0 K ohm resistor. Each drive has a termination
resistor located on the Main PCB. The terminator resistor is not removable and is always in the circuit.
Driver
2.0K Ohm [2]
+5V
- 48 mA (max).
Main PCB
Receiver
SYNC
REFIND +
GND
37
J1 - 37 [1]
J6 - 6
J6 - 5