DP83952 datasheet(21/90 Pages) NSC

21 / 90 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 pseudo ran-

dom data and jam signals 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 5-2 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

Inter-RIC bus If the repeater enters the

TRANSMIT COL-

LISION state a further arbitration operation is performed

to determine which port is

PORT M PORT M is differenti-

ated 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 II as shown in the block diagram

Figure

4-1 and it performs the majority of the data and collision

propagation operations as defined by the IEEE specifica-

tion

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 RIC IIs together In this configuration the logical func-

tion of a single repeater is maintained The resulting multi-

RIC II system is compliant to the IEEE 8023 repeater speci-

fication and may connect several hundred network seg-

ments An example of a multi-RIC II system is shown in

Figure 5-3

The Inter-RIC Bus connects multiple RIC IIs to realize the

following operations

Port N Identification (which port the repeater receives data

from)

Port M Identification (which port is the last one experiencing

a collision)

Data Transfer

RECEIVE COLLISION identification

TRANSMIT COLLISION identification

DISABLE OUTPUT (jabber protection)

Repeater Functions

Function

Action

Preamble

Restore the length of the preamble pattern to the defined size

Regeneration

Fragment

Extend received data or collision fragments to meet the minimum fragment length

Extension

of 96 bits

Elasticity

A portion of the received packet may require storage in an Elasticity Buffer to

Buffer Control

accommodate preamble regeneration

Jam

In cases of receive or transmit collisions a RIC II is required to transmit a jam

Preamble

pattern (1010) (Note)

Pattern

Generation

Transmit

Once the

TRANSMIT COLLISION state is entered a repeater is required to stay in

Collision

this state for at least 96 network bit times

Enforcement

Data

NRZ format data from the elasticity buffer must be encoded into Manchester

Encoding

format data prior to retransmission

Control

Tw1

Enforce the Transmit Recovery Time specification

Enforcement

Tw2

Enforce Carrier Recovery Time specification on all ports with active collisions

Enforcement

Note

This pattern is the same as that used for preamble regeneration

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