DP83950B datasheet(26/80 Pages) NSC

26 / 80 page

50 Functional Description (Continued)

Port State Machine (PSM)

There are two primary functions for the PSM as follows

1 Control the transmission of repeated data and jam sig-

nals over the attached segment

2 Decide whether a port will be the source of data or colli-

sion information which will be repeated over the network

This repeater port is known as

PORT N An arbitration

process is required to enable the repeater to transition

from the

IDLE state to the SEND PREAMBLE PATTERN

RECEIVE COLLISION states see Figure 53 This pro-

cess is used to locate the port which will be

PORT N for

that particular packet The data received from this port is

directed to the PLL decoder and transmitted over the In-

ter-RIC bus If the repeater enters the

TRANSMIT COLLI-

SION state a further arbitration operation is performed to

determine which port is

PORT M PORT M is differentiat-

ed from the repeater’s other ports if the repeater enters

the

ONE PORT LEFT state In this state PORT M does

not transmit to its segment where as all other ports are

still required to transmit to their segments

Main State Machine (MSM)

The MSM controls the operation of the shared functional

blocks in each RIC as shown in the block diagram

Figure

51 and it performs the majority of the data and collision

propagation operations as defined by the IEEE specifica-

tion these include

Function

Action

Preamble

Restore the length of the preamble

Regeneration

pattern to the defined size

Fragment

Extend received data or collision

Extension

fragments to meet the minimum

fragment length of 96 bits

Elasticity

A portion of the received packet may

Buffer

require storage in an Elasticity Buffer to

Control

accommodate preamble regeneration

Jam

In cases of receive or transmit collisions

Preamble

a RIC is required to transmit a jam

Pattern

pattern (1010)

Generation

Note

This pattern is the same as that used for

preamble regeneration

Transmit

Once the

TRANSMIT COLLISION state

Collision

is entered a repeater is required to stay

Enforcement

in this state for at least 96 network bit

times

Data

NRZ format data from the elasticity

Encoding

buffer must be encoded into Manchester

Control

format data prior to retransmission

Tw1

Enforce the Transmit Recovery Time

Enforcement

specification

Tw2

Enforce Carrier Recovery Time

Enforcement

specification on all ports with active

collisions

The interaction of the main and port state machines is visi-

ble in part by observing the Inter-RIC bus

Inter-RIC Bus Operation

Overview

The Inter-RIC Bus consists of eight signals These signals

implement a protocol which may be used to connect multi-

ple RICs together In this configuration the logical function

of a single repeater is maintained The resulting multi-RIC

system is compliant to the IEEE 8023 repeater specification

and may connect several hundred network segments An

example of a multi-RIC system is shown in

Figure 54

The Inter-RIC Bus connects multiple RICs to realize the fol-

lowing operations

Port N Identification (which port the repeater receives

data from)

Port M Identification (which port is the last one experienc-

ing a collision)

Data Transfer

RECEIVE COLLISION identification

TRANSMIT COLLISION identification

DISABLE OUTPUT (jabber protection)

The following tables briefly describes the operation of each

bus signal the conditions required for a RIC to assert a

signal and which RICs (in a multi-RIC system) would monitor

a signal

ACKI

Function

Input signal to the PSM arbitration

chain This chain is employed to

identify

PORT N and PORT M

Note

A RIC which contains

PORT N or

PORT M may be identified by its ACKO

signal being low when its ACKI input is

high

Conditions

Not applicable

required for a

RIC to drive

this signal

RIC Receiving

This is dependent upon the method

the signal

used to cascade RICs described in

a following section

ACKO

Function

Output signal from the PSM

arbitration chain

Conditions

This is dependent upon the method

required for a

used to cascade RICs described in

RIC to drive

a following section

this signal

RIC Receiving

Not applicable

the Signal

DP83950B Datasheet(PDF) 26 Page - National Semiconductor (TI)

DP83950B Datasheet(HTML) 26 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Datasheet Download

Link URL