DP83261AVF datasheet(21/132 Pages) NSC

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50 Functional Description (Continued)

572 Beacon Process

Receive

When a Beacon frame is received its Frame Type is report-

ed (Beacon frame) along with the type of Beacon frame

There are two types of Beacon frames My

Beacon and

Other

Beacon

A Beacon frame is considered a My

Beacon if its Source

Address matches this station’s address (long or short)

A Beacon frame is marked as Other

Beacon if its Source

Address does not match this station’s address

Transmit

Beacon frames are transmitted continuously while in the

Beacon state

Beacon frames are generated by the Ring Engine unless an

Immediate Beacon Request is present at the MAC Request

Interface Even if an Immediate Beacon Request is present

at the MAC Request Interface at least one Beacon frame

must be generated by the Ring Engine before Beacon

frames from the Interface are transmitted

For internally generated Beacon frames the Ring Engine

uses the TBT in the Information field

Beacon Protocol

Entry to the Beacon state occurs under two conditions

A failed Claim Process (TRT expires during the Claim

process)

An SM MA Controlrequest (Beacon)

(Set FunctionBCN to 1)

Beacon frames are then transmitted until the Beacon pro-

cess is completed

If an Other

Beacon frame is received this station exits the

Beacon state stops sending its own Beacon frames and

repeats the incoming Beacon frames

IfaMy

Beacon frame is received the station has received

back its own Beacon frame thus successfully completing

the Beacon process The station then enters the Claim Pro-

cess

573 Handling Reserved MAC Frames

A Reserved MAC frame is any MAC frame aside from the

Claim and Beacon frame Tokens are not considered MAC

frames even though Format bit (FCFF) are the same as for

MAC frames

When a Reserved MAC frame (Other

MAC) is received it

is treated as a Higher Claim If the Transmitter is in the

Claim state when a Reserved MAC frame is received the

Transmitter returns to the Idle state and then repeats the

next Reserved MAC frame received If the Transmitter is in

the Beacon state and a Reserved MAC frame is received

the Transmitter continues to transmit Beacon frames If the

Transmitter is in the Idle state the Reserved MAC frame is

repeated

58 RECEIVE BATCHING SUPPORT

The Ring Engine stores each received SA and compares

the incoming SA with the previous SA This may be used to

batch status on frames received from the same station

The SameSA signal is asserted when

1 The curent and previous non-Void frames were not MAC

frames

2 The size of the address of the current frame is the same

as the size of the address of the previous non-Void frame

3 The SA of the current frame is the same as the SA of the

previous non-Void frame

On MAC frames the Information fields are compared This

information may be useful to inhibit copying MAC frames

with identical information This is particularly useful for copy-

ing Claim and Beacon frames when new information is pres-

ent

The Same INFO signal is asserted when

1 The current and previous non-Void frames were both

MAC frames (not necessarily the same FC value)

2 The first four bytes of the INFO field of the current frame

is the same as the first four bytes of the INFO field of the

previous non-Void frame

The size of the address of MAC frames is not checked

59 IMMEDIATE FRAME TRANSMISSION

Immediate requests are used when it is desirable to send

frames without first capturing a token Immediate requests

are typically used as part of management processes for er-

ror isolation and recovery Immediate requests are also use-

ful in full duplex applications Immediate requests are serv-

iced only when the station’s Ring

Operational flag is not

set (CTSRROP e 0)

To transmit an Immediate request the request must first be

queued at the MA

Request Interface If the Ring is not

operational (Ring

Operational flag is not set) the request

will be serviced immediately If the Ring is operational

(Ring

Operational flag is set) the request will be serviced

when the Ring becomes non-operational The Ring be-

comes non-operational as a result of a MAC Reset

(FunctionMCRST is set to One) or any of the conditions

causing the Reset or Recovery Actions are performed

In addition to servicing an Immediate request from the

Data State it is also possible to service Immediate re-

quests from the Claim or Beacon State When transmitting

from the Claim or Beacon state in addition to requesting an

Immediate Transmission Service Class the RQCLM or

RQBCN signals (pins 15 and 16) must be asserted to indi-

cate an Immediate Claim or Immediate Beacon request

These requests will only be serviced when in the Claim or

Beacon state Entry to the Beacon State can be forced

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