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Seagate Enterprise Capacity 3.5 HDD v4 SAS Product Manual, Rev. D 63
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.
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 14 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 15.
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 16 for the output
characteristics of the LED drive signals.
Table 15 Ready LED Out conditions
Normal command activity LED status
Ready LED Meaning bit mode page 19h
01
Spun down and no activity Off Off
Spun down and activity (command executing) On On
Spun up and no activity On Off
Spun up and activity (command executing) Off On
Spinning up or down Blinks steadily
(50% on and 50% off, 0.5 seconds on and off for 0.5 seconds)
Format in progress, each cylinder change Toggles on/off
Receiver
Differential
Transfer Medium
.01
.01
100100
Transmitter
RX
RY
TX
TY