DP83266 datasheet(25/152 Pages) NSC

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50 Functional Description (Ring Engine) (Continued)

Additionally only the station that sets the A Indicator is per-

mitted to set the C Indicator on such frames In this way the

station that sends out the NSA frame can determine if the

next addressed station copied the frame by examining the

returning C Indicator

57 MAC FRAME PROCESSING

Upon the reception of a valid MAC frame (Claim Beacon or

Other) the Ring

Operational flag is reset and the Ring En-

gine enters the Idle Claim or Beacon State Received Claim

and Beacon frames are processed as defined in the MAC

Standard unless explicitly inhibited by the bits in the Option

571 Claim Token Process

Receive

When a Claim frame is received its Frame Type is reported

(Claim frame) along with the type of Claim frame

There are three types of Claim frames My

Claim Higher

Claim and Lower

Claim

AMy

Claim frame is a Claim frame with a Source Address

that matches this station address and the T

Bid

Rc in the

INFO field is equal to this station’s TREQ

A Higher

Claim frame is a Claim frame with a Source Ad-

dress that does not match this station address and the

Bid

Rc in the INFO field is greater than this station’s

TREQ

A Lower

Claim frame is a Claim frame with a Source Ad-

dress that does not match this station address and the

Bid

Rc in the INFO field is smaller than this station’s

TREQ

Transmit

Claim frames are transmitted continuously while in the

Claim State

Claim frames are generated by the Ring Engine unless an

Immediate Claim Request is present at the MAC Request

Interface Even if an Immediate Claim Request is present at

the MAC Request Interface at least one Claim frame must

be generated by the Ring Engine before Claim frames from

the Interface are transmitted

For internally generated Claim frames the Information field

is transmitted as the 4-byte Requested Target Token Rota-

tion Time

The Information field of a Claim frame consists of this sta-

tion’s Requested Target Token Rotation Time In the Ring

Engine implementation

TREQ is programmable with a

2048 ms resolution and a maximum value of 134 seconds

Claim Protocol

Entry to the Tx

Claim state occurs whenever token recov-

ery is required The Recovery Required condition occurs

when

TRT expires and Late Flag is set

TVX expires

A Lower Claim frame or My Beacon frame is received

Entry to the TX

Claim state may be blocked by enabling

the Inhibit Recovery Required option (bit OptionIRR)

The Tx

Claim state is entered (even if OptionIRR e 1)

with an SM

Controlrequest(Claim) which is accom-

plished by setting FunctionCLM to 1

While in the Tx

Claim state

Claim frames are transmitted continuously

If a Higher Claim frame is received the station exits the

Claim state and enters the IDLE state In this state it then

repeats additional Higher

Claim frames

If a Lower Claim frame is received this station contin-

ues to send its own Claim frames and remains in the

Claim state

Eventually if a logical ring exists the station with the short-

est TREQ on the ring should receive its own Claim frames

the My

Claim frame This completes the Claim Token Pro-

cess This one station then earns the right to issue a token

to establish an Operational ring

An option is provided to remain in the Claim state if this

station won the Claim Token Process by enabling the Inhibit

Token Release Option (bit OptionIRR)

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 Tx

Beacon state occurs under two conditions

A failed Claim Process (TRT expires during the Claim

process)

An SM MA Controlrequest(Beacon) which is accom-

plished by setting 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

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