SBPH400-3 datasheet(16/43 Pages) STMICROELECTRONICS

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SBPH400-3

The SBPH400 has control over the bidirectional pins. It will, upon request, transfer this control

to the link device, which can then drive these pins. The 8 bidirectional data pins D[0:7] form

the data bus. The portion of the D bus which carries packet data is left-justified starting with

the 0 bit. Packet data for 100 Mb/s transfers uses D[0:1], 200 Mb/s transfers use D[0:3], and

400 Mb/s transfers use D[0:7]. The unused D[n] signals are transmitted as ‘0’ and are ignored

when the link device has control of the bus. The control bus CTL[0:1] carries the control

information. The LREQ pin is used by the link device to request access to the serial bus and

to read and write the chip registers.

2.8.2 Types of operation

The four basic operations which may occur at the PHY-Link interface are: request, status,

transmit and receive. Request is the only operation initiated by the link layer device. The link

layer device uses the request operation to read or write a register located in the SBPH400 or

to request the bus so that the SBPH400 can initiate a transmit action on the bus. The

SBPH400 initiates a receive action whenever a packet is received from the serial bus and a

status indication to notify events to the link layer device.

2.8.3 Control pins

When the SBPH400 has control of the PHY-Link interface the CTL[0:1] lines are encoded as

shown in Table 2.5.

When the link layer device has been granted the PHY-Link interface by the SBPH400, it should

encode the CTL[0:1] lines Table 2.6

Table 2.5

CTL[0:1] When the SBPH400 is driving

CTL[0:1]

NAME

DESCRIPTION

Idle

No activity (default mode)

Status

The SBPH400 is sending status information to the link device

Receive

An incoming packet is being transferred from the SBPH400 to the link

device

Grant

The link device is granted the bus to send a packet

Table 2.6

CTL[0:1] when the link is driving (upon grant from SBPH400)

NAME

DESCRIPTION

Idle

The link device has released the bus (normally after transmission).

Note that multiple Idles may need to be transmitted.

Hold

The link device is preparing data or wishes to reacquire the bus without

arbitrating to send another packet

Transmit

The link device is sending a packet to the SBPH400

unused

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