DP83953 datasheet(17/90 Pages) NSC

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4.0 Functional Description (Continued)

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The Port State Machine (PSM)

The two primary functions of the PSM are to:

1. Control the transmission of repeated data, pseudo ran-

dom data, and jam signals over the attached segments.

2. Determine if a port will be the source of data or collision

information to be repeated over the network. This repeat-

er port is known as

PORT N. An arbitration process is re-

quired to enable the repeater to transition from an

IDLE

state to the

SEND PREAMBLE PATTERN or RECEIVE

COLLISION states. (See Figure 4) This process is used

to locate the port that will be

PORT N for that particular

packet.The data received from

PORT N is directed to the

PLL decoder and transmitted over the Inter-RIC bus. If a

collision occurs, the repeater enters the

TRANSMIT

COLLISION state. Then a subsequent arbitration opera-

tion is performed in order to determine which port is

PORT M. PORT M is differentiated 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 seg-

ment. At that time, all other ports are still required to

transmit to their segments.

The Main State Machine (MSM)

The MSM controls the operation of the shared functional

blocks in each RIC2A as shown in the block diagram,

Figure 1, and performs the majority of the data and colli-

sion operations as defined by the IEEE specification.

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

ble, in part, through the Inter-RIC bus.

Inter-RIC Bus (IRB) Operation

Overview

The IRB consists of eight signals. These signals implement

a protocol that may be used to connect multiple RIC2As

together. In this configuration, the logical function of a sin-

gle repeater is maintained. The resulting multi- RIC2A

repeater system is compliant with the IEEE 802.3 Repeater

Specification and may even encompass several hundred

network segments. Figure 5 shows an example of a multi-

port RIC2A system.

Function

Action

Preamble

Regeneration

Restore the length of the preamble pat-

tern to the defined size.

Fragment

Extension

Extend received data or collision frag-

ments to meet the minimum fragment

length of 96 bits.

Elasticity Buffer

Control

A portion of the received packet may re-

quire storage in an Elasticity Buffer to

accommodate preamble regeneration.

Jam / Preamble

Pattern Genera-

tion

In cases of receive or transmit colli-

sions, a RIC2A is required to transmit a

jam pattern (1010...).

Note: This pattern is the same as that used for pre-

amble regeneration.

Transmit

Collision

Enforcement

The

TRANSMIT COLLISION state re-

quires a repeater to remain in this state

for at least 96 bit times.

Data Encoding

Control

NRZ formatted data in the elasticity

buffer must be encoded into Manches-

ter formatted data prior to re-transmis-

sion.

Tw1

Enforcement

Enforce the Transmit Recovery Time

specification.

Tw2

Enforcement

Enforce Carrier Recovery Time specifi-

cation on all ports with active collisions.

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