Fujitsu MBC2036RC, MBC2073RC, MBA3300RC Phy layer, 1 8b10b coding, Usage of special characters

1.3 Phy layer

1.3 Phy layer

In the phy layer, 8b10b coding and the link reset sequence are defined.

1.3.1 8b10b coding

All information transferred in SAS is encoded into 10-bit characters using 8b10b encoding. Information includes data bytes representing data in a frame and control characters used for frame delimiters.

Ten-bit characters are transferred in units of dwords, where a dword contains four ten-bit characters.

A primitive is a dword that consists of a control character at the beginning and the other three data characters.

In the SAS specifications, a primitive that starts with the K28.5 control character and another one that starts with the K28.6 control character are defined. Table 1.3 shows the usage of special characters.

Table 1.3 Usage of special characters

Beginning character	Usage in SAS	Usage in SATA
K28.3	Primitive to be used only within STP	All the primitives
	connection	except ALIGN
K28.5	ALIGN and most primitives that are	ALIGN
	defined in SAS
K28.6	SATA_ERROR	Not used.
	(used on the physical link layer of SATA)
Dxx.y	Data	Data

A single data dword is a dword that starts with a data character.

Running disparity shall be maintained separately on each physical link. During a connection, expander devices shall convert incoming 10-bit characters to 8-bit bytes and generate the 10-bit character with correct disparity for the output physical link. Phys within a device may or may not begin operation with the same disparity after the reset sequence.

Information to be transmitted across a physical link shall be encoded eight bits at a time into a 10-bit character and then transmitted serially bit-by-bit across the physical link. Information received over the physical link shall be collected ten bits at a time, and those characters that are used for data, called data characters, shall be decoded into the correct 8-bit data bytes. The 10-bit characters support all 256 8-bit combinations. 8b10b coding ensures that sufficient transitions are present in the serial bit stream to make clock recovery possible at the receiver. Such encoding also greatly increases the likelihood of detecting any single or

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