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CHEETAH 15K.7 SAS PRODUCT MANUAL, REV. F 51
11.4.6 SAS transmitters and receivers
A typical SAS differential copper transmitter and receiver pair is shown in Figure 15. The receiver is AC coupling to eliminate
ground shift noise.
Figure 15. 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 13 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 14.
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 15 for the output characteristics of the LED drive signals.
Table 14 Ready LED Out conditions
NORMAL COMMAND ACTIVITY LED STATUS
Ready LED Meaning bit mode page 19h 0 1
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 Toggles on/off
Write Same command in progress Toggles on/off