9.4.6SAS transmitters and receivers

A typical SAS differential copper transmitter and receiver pair is shown in Figure 17. The receiver is AC cou- pling to eliminate ground shift noise.

 

TX

Transmitter

Differential

Transfer Medium

100

 

 

TY

Figure 17. SAS transmitters and receivers

.01

.01

RX

Receiver

100

RY

9.4.7Power

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 sup- ply 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.

9.5Signal characteristics

This section describes the electrical signal characteristics of the drive’s input and output signals. See Table 25 for signal type and signal name information.

9.5.1Ready LED Out

The Ready LED Out signal is driven by the drive as indicated in Table 26.

Table 26: 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

 

 

 

 

Cheetah 15K.6 SAS Product Manual, Rev. B

67

Page 71
Image 71
Seagate ST3146756SS (FDE), ST3146854LC manual Signal characteristics, SAS transmitters and receivers, Power, Ready LED Out