TNETE2008

OctalPHY

EIGHT 10BASE-T PHYSICAL-LAYER INTERFACES

SPWS042B – DECEMBER 1997 – REVISED JUNE 1998

14

POST OFFICE BOX 655303

synchronous PHY interface

To ease the pin-count burden on switching-application devices, Texas Instruments developed a multiplexed

interface, which allows multi-PHY devices to be connected to switching cores without using many terminals.

To achieve the reduction in terminal count, the interface takes advantage of the fact that modern silicon is able

to operate at frequencies much higher than the 10-MHz data rate of the standard interface.

The receive and transmit data are transferred over a nibble-wide bus, (see Figure 5). Table 1 describes the

signals on the interface. Any given port only transfers data at 2.5 MHz (2.5 MHz

× 4 bits = 10 Mbit/s). The

remaining control and status signals are sampled at the reduced rate of 2.5 MHz.

PHY

MAC

IFCLK

IFSYNC

IFCOL

IFCRS

IFLINK

IFDUPLEX

IFRXD3–IFRXD0

IFRXDV

IFTXD3–IFTXD0

IFTXEN

IFFORCEHD

CLK

SYNC

COL

CRS

LINK

DUPLEX

RXD3–RXD0

RXDV

TXD3–TXD0

TXEN

FORCEHD

Figure 5. Multiplexed 17-Pin Interface for Eight Ports

The interface runs synchronously to a TNETE2008 generated clock. The information (MAC

→ TNETE2008)

for the first port (port 0) is presented on the interface when IFSYNC is high; the next clock cycle the interface

carries the information for the second port. This process continues with each port using the interface for one

cycle. When all ports have been processed in this manner, the sequence resumes with the first port and again

IFSYNC is asserted. To improve latency-related issues, the data from the TNETE2008 to the MAC is skewed

by two slots as shown by the dashed line in Figure 6. This allows the MAC to respond to input signals from the

TNETE2008 in the same 400-ns cycle, rather than waiting for the next 400-ns cycle, which would be the case

if the signals were not skewed.

If the mode to be advertised during autonegotiation arrives on IFTXD3–IFTXD0 during link-invalid, IFFORCEHD

can be tied high or used to restart autonegotiation.