DP83266 datasheet(54/152 Pages) NSC

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70 Control Information (Continued)

Option Register (Option)

The Ring Engine supports several options These options are typically static during operation but may be altered during

operation This register is initialized to Zero after a master reset

Access Rules

Address

Read

Write

001h

Always

ITC

EMIND

IFCS

IRPT

IRR

ITR

ELA

ESA

Bit

Symbol

Description

ITC

Inhibit Token Capture

When enabled the Ring Engine is prohibited from transmitting any (more) frames

This option prohibits entry to the Transmit Void and Data states from the Idle state and causes exit from the

Data state after the current frame has been transmitted

When enabled it is still possible to perform Immediate transmissions from the transmitter Claim and Beacon

states but not from the Data state

This option can be used to temporarily block normal data service It can also be used in conjunction with the

Inhibit Recovery Required option to permit access via the Control Interface to the MAC Parameter RAM during

MAC operation

EMIND

External Matching Indicators

Enables the setting of the transmitted A Indicator as an S symbol when the EA

pin is set This bit also enables the setting of the transmitted C Indicator as an S symbol when the internal

VCOPY signal is asserted by the System Interface and the A Indicator is set as a result of an external match

(ie the User asserts the EA pin) The CopiedNot Copied Frame Counters also increment as a result of

external comparisons when this option is enabled

IFCS

Implementer FCS

Enables use of the standard CRC as the FCS on Implementer frames (FCFF e 10) When

enabled Implementer frames are treated like all other frames When Implementer frames are received with

bad FCS and Er e R the E Indicator is transmitted as S and EICT is incremented

On Implementer frames the Standard does not mandate the setting of the E Indicator on the result of the FCS

check This allows Implementers to use alternate Frame Check Sequences aside from the standard 32-bit

CRC Implementers may also choose not to use any FCS in applications such as packet voice

If other stations in the ring are using Implementer frames with a non-standard FCS this option may cause an

interoperability problem

IRPT

Inhibit Repeat

When enabled

1 the Ring Engine cannot enter the Transmitter Repeat and Issue

Token states This causes all received

PDUs to be stripped and prevents tokens from being issued

2 Void frames are not transmitted during a service opportunity

3 Idle to Repeat transition is inhibited and all received tokens and MAC frames except LowerClaim and

Beacon frames are ignored (Lower

Claim and My

Beacon frames may be ignored by setting

OptionIRR)

When the ring is operational enabling this option causes the Reset actions to occur upon the completion of

the service opportunity if any When the ring is not operational Immediate Requests are serviced and

continue to completion

The Inhibit Repeat option can be used to scrub the ring for a period longer than the Ring Latency The option is

also useful in non-FDDI applications to allow full duplex communication

DP83266 Datasheet(PDF) 54 Page - National Semiconductor (TI)

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