VT6306 datasheet(44/59 Pages) VIA

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VT6306 PCI 1394a Host Controller

Revision 1.16 July 19, 2002

-38-

Functional Descriptions

FUNCTIONAL DESCRIPTIONS

PHY General Description

Cable Interface

The VT6306 provides three-port physical layer function in a cable IEEE 1394-1995 network. Each cable port incorporates two

differential line transceivers. The transceivers include circuitry to monitor the line conditions as needed for determining connection

status, for initialization and arbitration, and for half duplex packet reception and transmission.

Data bits to be transmitted through the cable ports are latched internally in the VT6306 in synchronization with the 49.152-MHz

system clock. During transmission the encoded data is transmitted differentially on the TPB cable pair(s) and the encoded strobe

information is transmitted differentially on the TPA cable pair(s).

During packet reception, the TPA and TPB transmitters of the receiving cable port are disabled, and the receivers for that port are

enabled. The encoded data information is received on the TPA cable pair, and the encoded Strobe information is received on the

TPB cable pair. The received data-strobe information is resynchronized to local PLL clocks and the retiming buffer can tolerate

clock variation up to +/-100ppm with 4K bytes at 393.216 Mbps, 2K bytes at 196.608 Mbps, and 1K bytes at 98.304 Mbps.

Both the TPA and TPB cable interfaces (see figure below) incorporate differential comparators to monitor the line states during

initialization and arbitration. The outputs of these comparators are used by internal logic to determine the arbitration status. The

TPA channel generates the cable common-mode voltage. The value of this common mode voltage is used during arbitration to

detect the speed of the next packet transmission by the peer PHY. In addition, VT6306 adds a current source and a connection

detect circuit at TPA channel. When TPBIAS is driven low, the connection detect circuit is used to detect the presence or absence

of a peer PHY at the other end of a cable connection. The TPB channel monitors the incoming cable common-mode voltage for

the presence of the remotely supplied twisted-pair bias voltage. The presence or absence of this common-mode voltage is used as

an indication of cable suspend, resume and active status.

Figure 5. Cable Interface

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