The SATA interface is the connecting component between the hard disk and the host system, which is used to transfer data between the hard disk cache and the host memory. The different hard disk interfaces determine the connection speed between the hard disk and the computer. In the entire system, the quality of the hard disk interface directly affects the speed of program operation and system performance.
1、 SATA Interface Introduction
SATA (Serial ATA) is an abbreviation for Serial ATA, which is a new type of hard disk interface completely different from parallel ATA.
The SATA interface uses embedded clock signals and has stronger error correction capabilities. Compared with the past, its biggest difference is that it can check transmission instructions (not just data), and automatically correct errors if found, which greatly improves the reliability of data transmission.
The SATA interface will only transmit one bit of data at a time, which can reduce the number of pins, reduce the number of connecting cables, and improve efficiency; And SATA has a higher starting point and greater development potential. The data transfer rate defined by SATA1.0 can reach 150MB/sec, which is higher than the highest 133MB/sec data transfer rate that can be achieved by the fastest parallel ATA (i.e. ATA/133). Currently, the data transfer rate of SATA2.0 has reached 300MB/sec.
2、 SATA interface pin definition
1. Grounding (GND)
The grounding wire of the SATA interface is pin1, which is usually used to ground the device casing and provide low-level voltage to the interface.
2. Data+
The data main line of SATA interface is pin2, which is usually used for transmitting data signals and power supply of devices.
3. Data negative (Data -)
The data negative line of the SATA interface is pin3, which is usually used to return the data signal and power supply of the device.
It is worth noting that
The definition of pins is the same between different SATA devices, making it possible to connect SATA between different devices.
At the same time, the SATA interface also supports hot swapping function, which allows devices to be plugged and unplugged under constant power.
In addition, for 2.5-inch laptop serial hard drives, the+12V pin (i.e. the back three pins) is usually suspended and cannot be directly connected to the power adapter or power plug.
3、 SATA interface PCB design
1. Differential impedance
The differential impedance of SATA differential pairs must be 100 ohms. If the impedance does not match, it will cause unstable signal transmission and increase the bit error rate.
Therefore, in PCB design, it is necessary to ensure impedance matching of differential pairs through matching circuits or designing line impedance.
2. Differential line for wiring
The wiring requirements for differential pairs are very high, and attention should be paid to the length, width, spacing, and through holes of the wiring.
In PCB design, the routing of differential pairs should be close and of equal length, with a spacing of 6 to 10 times the line width. It is recommended to use microstrip lines. If the routing of differential pairs must be in different layers, the routing length on both sides of the through-hole must be consistent. In addition, it is necessary to avoid differential pairs being too close to other signals to avoid crosstalk.
3. EMI and crosstalk
Due to the high transmission speed of the SATA interface, it can generate EMI (electromagnetic interference) and crosstalk. To reduce EMI and crosstalk, the following points need to be noted.
The spacing between differential pairs of lines should not exceed 150mil; The routing of differential pairs should not be too close, and it is recommended that the spacing between the routing should be 6 to 10 times the height of the routing relative to the reference plane (preferably 10 times); Avoid using test points on differential signals with gigabit transmission speed; The distance between other signals on the same layer and differential signal pairs should be at least 10 to 15 times the height of the routing relative to the reference plane.
4. Power and ground
The SATA interface requires stable power and ground supply.
In PCB design, it is necessary to provide a dedicated power layer and ground layer for the interface, and ensure the continuity of power and ground.
5. Test points and maintenance
For the convenience of testing and maintenance, it is necessary to design some testing points at the interface, such as power testing points, ground testing points, and signal testing points.
The location and number of test points should be designed according to actual needs, without affecting the normal operation of the interface.
4、 Design for Manufacturability of SATA Interface PCB
1. Impedance line
In the manufacturing process, the tolerance for impedance lines is+/-10%, while for ordinary wiring, it is generally+/-20%. Impedance lines require more precision, so it is best to design impedance lines that are greater than the minimum production capacity of ordinary lines.
2. Pin holes
The pin holes of SATA interface devices should be of appropriate size. Plugins with larger apertures may become loose, while smaller apertures may prevent the device from being inserted.
3. Solder pads
The PCB pads for SATA interfaces should be of appropriate size for easy soldering and maintenance.
4. Testing
For the convenience of testing and debugging, test points or test ports should be reserved on the PCB
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