DP83266 datasheet(16/152 Pages) NSC

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40 FDDI MAC Facilities (Continued)

TABLE 4-6 Void Frames

Type

Enable

Size

SFS

FCS

EFS

Void

ESA

Short

null

MSA

FCS

TRRR

Void

not ESA

Long

null

MLA

FCS

TRRR

Void

ESA

Short

MSA

FCS

TRRR

Void

not ESA

Long

MLA

FCS

TRRR

TABLE 4-7 Claim Frames

Type

Enable

Size

SFS

INFO

FCS

EFS

Claim

not ELA

Short

MSA

TREQ

FCS

TRRR

Claim

ELA

Long

MLA

TREQ

FCS

TRRR

TABLE 4-8 Beacon Frames

Type

Enable

Size

SFS

INFO

FCS

EFS

Beacon

not ELA

Short

null

MSA

TBT

FCS

TRRR

Beacon

ELA

Long

null

MLA

TBT

FCS

TRRR

When the Transmit Beacon State is entered from the Trans-

mit Claim State the first byte of the 4 byte TBT field is trans-

mitted as Zero

Beacon frames that require alternative formats such as Di-

rected Beacons must be generated externally

The Ring Engine detects reception of valid Beacon frames

and distinguishes between Beacon frames transmitted by

this MAC (My

Beacon) and Beacon frames transmitted by

other stations (Other

Beacon)

43 FRAME COUNTS

To aid in fault isolation and to enhance the management

capabilities of a ring the Ring Engine maintains several

frame counts The Error and lsolated frame counts incre-

ment when a frame is received with one or more errors that

were previously undetected The Ring Engine then modifies

the Error Control Indicator so that a downstream station will

not increment its count

The size of the counters has been chosen such that minimal

software intervention is required even under marginal oper-

ating conditions

The following counts are maintained by the Ring Engine

FRCT

Frame Received

ElCT

Error lsolated

LFCT

Lost Frame

FCCT

Frames Copied with Ax set

FNCT

Frames Not Copied with Ax set

FTCT

Frames Transmitted

431 Frame Received Count (FRCT)

The Frame Received Count is described in the FDDl MAC

standard and is the count of all complete frames received

This count includes frames stripped by this station

432 Error lsolated Count (ElCT)

The Error lsolated Count is described in the FDDl MAC stan-

dard and is the count of error frames detected by this sta-

tion and no previous station It increments when

1 An FCS error is detected and the received Error Indicator

(Er) is not equal to S

2 A frame of invalid length (ie off boundary T) is received

and Er is not equal to S

3 Er is not R or S

433 Lost Frame Count (LFCT)

The Lost Frame Count is described in the FDDl MAC stan-

dard and is the count of all instances where a format error

is detected in a frame or token such that the credibility of

reception is placed in doubt The Lost Frame Count is incre-

mented when any symbol other than data or Idle symbols is

received between the Starting and Ending Delimiters of a

frame (this includes parity errors)

434 Frame Copied Count (FCCT)

The Frame Copied Count is described in the FDDl MAC

standard and is the count of the number of frames ad-

dressed to and copied by this station The count is incre-

mented when an internal or external match occurs (when

OptionEMlND enabled) on the Destination Address no er-

rors were detected in the frame and the frame was success-

fully copied (which the Service Engine communicates to the

Ring Engine via the internal VCOPY signal) Frames copied

promiscuously MAC frames Void frames and NSA frames

received with the A indicator set are not included in this

count

DP83266 Datasheet(PDF) 16 Page - National Semiconductor (TI)

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