TNETE2008

OctalPHY

EIGHT 10BASE-T PHYSICAL-LAYER INTERFACES

SPWS042B – DECEMBER 1997 – REVISED JUNE 1998

11

POST OFFICE BOX 655303

polarity reversal

The TNETE2008 can detect reversed polarity of its receiver inputs (e.g., due to incorrect cable wiring). If at any

time, seven consecutive inverted link pulses are detected, then, reversed polarity is assumed, and the octal

swaps the RCVP and RCVN inputs of the affected PHY. Once a single, correct link pulse is received, good

polarity is assumed.

autonegotiation

The TNETE2008 supports IEEE Std 802.3 autonegotiation to full duplex where allowed by a link partner. Each

PHY on the device is capable of independent autonegotiation. When enabled, this feature allows a PHY to

negotiate with the other PHY on its link segment, to establish their highest common protocol. Until a PHY has

completed its negotiation, it does not assert IFLINK.

When autonegotiation is disabled for a PHY, via the extended multiplexed MAC interface, link is indicated on

receipt of valid data or link pulses.

loopback test mode

By asserting the LOOPBACK terminal on the device, the transmit circuit of each PHY is looped to the

corresponding receive circuit; therefore, transmit drivers do not forward any further packet data to the network

but continue to send link pulses.

Since there is only one LOOPBACK terminal on the package, all eight PHYs simultaneously are placed into

loopback mode.

While in loopback mode, all network receive activity, other than the link pulses, is ignored. However, squelch

information is still processed, allowing the link status to be maintained under momentary loopback self-test.

During loopback, IFLINK is driven high for all channels, regardless of the state of the links on all channels. When

LOOPBACK goes high, the true state of link on each channel is reported.

Although the TNETE2008 places no restrictions on the format of transmitted data, looped-back data should

begin with a preamble and a start-of-frame delimiter to avoid spurious behavior of the receive-data recovery

circuitry.