AX88850

PRELIMINARY

ASIX ELECTRONICS CORPORATION

19

3.0 Functional Description

3.1 PCS interface logic

The PCS logic performs PCS / MII receiving / transmitting interface. When it receives, first deciphers the signals from

RDATA<4:0>, then do symbol alignment after detecting /J/K/ codes, then data is aligned to do 5B/4B decoding.

When it transmits, first do 4B/5B encoding to convert MII signals to PCS signals, then enciphers and send to

TDATA<4:0>.

When RSD is high from low, then link fail counter will count for 330u sec, then the port can receive packet normally.

During 330u sec that link fail counter counts, then receiving packet will be ignored. Cipher / No-cipher is selected by

station management access logic.

3.2 Carrier Integrity Monitor State Machine ( AX88853 PCS mode only )

For 100BASE-X systems, it is necessary that the repeater set protect the network from some transient fault conditions

that would disrupt network communications. Potential likely causes of such conditions are DTE and repeater power-

up and power-down transients, cable disconnects, and faulty wiring.

The AX88853 support CIM state machine with self-interrupt capability to prevent a segment’s spurious carrier

activity from reaching the repeater unit and hence propagating through the network.

3.3 Repeater State Machine

The repeater state machine is used to control repeater behavior, generates right signal in corresponding states. The

repeater state machine is in Idle state when there is no carrier . When

there is carrier , the repeater state machine

goes to Data Forwarding State to ensure correct data forwarding. If collision happens anytime, The repeater state

machine detects collision then send jam pattern until collision ceases.

idle State

The idle state happens when these conditions exists:

a.

/RST is low.

b.

Reset emitted by station management access logic(RST_RSM).

c.

There is no any carrier in M0_CRS[7:0], M1_CRS[7:0], and CRS{1:0] in MII mode. Or

receive IDLE code in PCS mode. If in cascade application, repeater receive no inter repeater

active signal.

In this state,M0_RXEN[7:0],M1_RXEN[7:0],M0_TXEN[7:0],M1_TXEN[7:0] are all low in MII

mode.

Data Forwarding State

When there is only one carrier in M0_CRS[7:0], M1_CRS[7:0]or CRS[0], CRS[1] in MII mode, or

only one of eight ports receives /J/K/ codes in PCS mode ,or only one of IR_ACTO[7:0] become low,

The repeater state machine stores receiving packet and transmits to all other ports. Exception for

a.

The port is jabbered.

b.

The port is partitioned.

c.

There exists collision.

In this state, only one of M0_RXEN[7:0] and M1_RXEN[7:0] is high, or M0_RXEN[7:0] or

M1_RXEN[7:0] are all low because either packet is from two dedicated MII port or from inter-repeater

cascade interface in MII mode.

The repeater send packet from receiving port to all ports exclusive of the receiving that is

M0_TXEN[7:0] and M1_TXEN[7:0] all becomes high, and one may be low if that port is the receiving

port in MII mode. The repeater forwards data to TDATA[7:0] except for the receiving RDATA port in

PCS mode.