DP83261 datasheet(28/132 Pages) NSC

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60 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

01h

Always

ITC

EMIND

IFCS

IRPT

IRR

ITR

ELA

ESA

Bit

Symbol

Description

ESA

Enable Short Addressing

Enables the setting of A

Flag on matches of received Short Destination

Addresses with MSA Enables the setting of M

Flag and stripping on matches of received Short Source

Addresses with MSA

Permits transmission of frames with Short Addresses Frames with Short Addresses can be transmitted when

Short Addressing is not enabled if the SA Transparency option is selected

Void frames are sent with the Short Address if ESA is set to One If ESA is Zero and ELA is One Void frames

are sent with the Long Address

When both the ESA and ELA bits are Zero the ring is effectively interrupted at this station The token capture

process and Error Recovery logic are suspended and no frames are repeated Immediate requests are

serviced if the SA Transparency option is selected

ELA

Enable Long Addressing

Enables the setting of A

Flag on matches of received Long Destination

Addresses with MLA Enables the setting of M

Flag and stripping on matches of received Long Source

Address with MLA

Permits transmission of frames with Long Addresses Frames with long addresses can be transmitted when

long addressing is not enabled if the SA transparency option is selected

Claim and Beacon frames are sent with the Long Address if ELA is One If ELA is Zero and ESA is One Claim

and Beacon frames are sent with the Short Address

When both ESA and ELA are Zero the ring is effectively interrupted at this station The token capture process

and Error Recovery logic are suspended and no frames are repeated Immediate requests are serviced if the

SA Transparency option is selected

ITR

Inhibit Token Release

When bit ITR is set to One the station will not issue a token after winning the Claim

Process The station remains in the Claim state while the station’s Claim frames are returning to the station

and it has won the Claim Process At this point the station is in control of the ring as long as no Higher

Claim

or Beacon frames are received

While in control of the ring the station may transmit special Claim or Management frames for a variety of

implementation specific purposes For example the station might send out a Claim frame with a unique

identifier to make sure that another station with its address and TREQ is not also Claiming

IRR

Inhibit Recovery Required

When bit IRR is set to One the Ring Engine does not take the transitions into the

Claim state (T4) This option inhibits all the recovery required transitions as defined in the FDDI MAC Standard

This bit does not inhibit entry to the Claim state on a Claim Request generated at the MAC Request Interface

via the Function Register

This option can be used to guarantee that implementation specific Beacon frames will be transmitted from the

Beacon state It is also useful in systems where Local Address Administration is used to prohibit stations with

the Null Address (or any address) from Claiming The option could also be used to enable the use of the Ring

Engine in full duplex applications (in conjunction with the Inhibit Repeat option) to disable the recovery timers

DP83261 Datasheet(PDF) 28 Page - National Semiconductor (TI)

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