DP83266 datasheet(56/152 Pages) NSC

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70 Control Information (Continued)

Function Register (Function)

The Ring Engine performs the MAC Reset Claim Request and Beacon Request using the Function Register The Register is

initialized to Zero after a master reset A function is performed by setting the appropriate bit to One When the function is

complete the bit is cleared by the Ring Engine

Access Rules

Address

Read

Write

002h

Always

RES

CLM

BCN

MCRST

RES

MARST

Bit

Symbol

Description

D7 – D5

RES

Reserved

CLM

Claim Request

Produces the functions equivalent to an SM

CONTROLrequest (Claim) and causes

entry to the Tx

Claim State The Ring Engine Transmitter is forced to enter the Tx

Claim State unless

the Transmitter is in the Tx

Beacon State or bit BCN is set to One Claim frames are then transmitted

until the Claim process completes The Claim process will not complete if OptionITR e 1

A Claim Request is honored immediately from any state except the Beacon state It is honored in the

Beacon state when a My

Beacon returns Claim requests are honored even when OptionIRR e 1

Claim frames are generated by the Ring Engine unless an Immediate Claim Request is available at the

MAC Request Interface Even with an Immediate Claim Request at the Interface the Ring Engine

transmits at least one Claim frame before the Claim frames from the MAC Request Interface are

transmitted

If an external Claim frame is to be transmitted the Claim frame should first be set up then the request

should be given to the MAC Request Interface before the CLM bit is set to One

The CLM bit is reset upon entry to the Claim or Beacon state

BCN

Beacon Request

Produces the functions of an SM

CONTROLrequest (Beacon) as required by the

FDDI MAC Standard The Ring Engine Transmitter is forced to enter the Tx

Beacon State Beacon

frames are then transmitted until the Tx

Beacon Process completes The Beacon Process will not

complete if OptionIRR e 1

Beacon frames are generated by the Ring Engine unless an Immediate Beacon Request is present at the

MAC Request Interface and a frame is ready to be transmitted Even with an External Immediate Beacon

Request the Ring Engine transmits at least one Beacon frame before the Beacon frames from the MAC

Request Interface are transmitted

If an external Beacon frame is to be transmitted the Beacon frame should first be set up via the System

Interface and then bit BCN should be set to One

Setting this bit also sets bit D2 (MCRST) The BCN bit is cleared on entry to the Beacon state If the User

programs both D3 (BCN) and D4 (CLM) simultaneously bit D3 (BCN) takes precedence

MCRST

MAC Reset

Forces the Receiver to state R0 (Listen) and the Transmitter to state T0 (Idle)

TNEG (Registers 098 – 09B) is not loaded with TMAX (this operation can be performed as part of the MAC

Reset Request actions by writing to TNEG Timers before the MAC Reset is initiated)

MCRST takes precedence over bits D3 (BCN) and D4 (CLM) but does not clear these bits

A MAC Reset that occurs while a frame is being transmitted will cause the frame to be aborted Frames

without the Frame Status are not transmitted by the Ring Engine Whenever the byte with the Ending

Delimiter is transmitted valid frame status is transmitted as well If a MAC Reset occurs during the byte

where the Ending Delimiter and E Indicator should be transmitted it will not be transmitted If a MAC Reset

occurs on the cycle where the A and C Indicators are transmitted they will still be transmitted

RES

Reserved

MARST

Master Reset

A Master Reset is functionally equivalent to a hardware reset of the Ring Engine (MAC) A

Master Reset sets all Ring Engine state machines and registers to default values

Master Reset causes the MCRST bit to be set It also clears the Mode Option Event and Mask Registers

The Timers are set to their defaults The Counters are not cleared

When the Master Reset function is complete bit D0 (MARST) is set to Zero At this time all bits in the

Function Register should be Zero

DP83266 Datasheet(PDF) 56 Page - National Semiconductor (TI)

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