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11.4.6 SAS transmitters and receivers
A typical SAS differential copper transmitter and receiver pair is shown in Figure 20. The receiver is AC coupling to eliminate ground shift
noise.
TX
Transmitter
100
TY
Figure 20.
SAS transmitters and receivers
11.4.7 Power
The drive receives power (+5 volts and +12 volts) through the SAS device connector.
Three +12 volt pins provide power to the drive, 2 short and 1 long. The current return for the +12 volt power supply is through the common
ground pins. The supply current and return current must be distributed as evenly as possible among the pins.
Three +5 volt pins provide power to the drive, 2 short and 1 long. The current return for the +5 volt power supply is through the common
ground pins. The supply current and return current must be distributed as evenly as possible among the pins.
Current to the drive through the long power pins may be limited by the system to reduce inrush current to the drive during hot plugging.
11.5
Signal characteristics
This section describes the electrical signal characteristics of the drive's input and output signals. See Table 15 for signal type and signal
name information.
11.5.1 Ready LED Out
The Ready LED Out signal is driven by the drive as indicated in Table 16.
Table 16 Ready LED Out conditions
Normal command activity
Ready LED Meaning bit mode page 19h
Spun down and no activity
Spun down and activity (command executing)
Spun up and no activity
Spun up and activity (command executing)
Spinning up or down
Format in progress, each cylinder change
The Ready LED Out signal is designed to pull down the cathode of an LED. The anode is attached to the proper +3.3 volt supply through
an appropriate current limiting resistor. The LED and the current limiting resistor are external to the drive. See Table 17 for the output
characteristics of the LED drive signals.
Seagate Enterprise Capacity 3.5 HDD v4 SAS Product Manual, Rev. B
01
Differential
Transfer Medium
01
0
Off
On
On
Off
(50% on and 50% off, 0.5 seconds on and off for 0.5 seconds)
RX
Receiver
100
RY
LED status
Blinks steadily
Toggles on/off
1
Off
On
Off
On
65
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