DP83261AVF datasheet(19/132 Pages) NSC

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50 Functional Description (Continued)

55 FRAME STATUS PROCESSING

Each frame contains three or more Control Indicators The

FDDI Standard specifies three the E A and C Indicators

When a frame is transmitted the Control Indicators are

transmitted as R (Reset) symbols If an error is detected by

a station that receives the frame the E Indicator is changed

to an S (Set) symbol If a station recognizes the DA of a

frame as its own address (Individual Group or Broadcast)

the A Indicator is changed to an S symbol If that station

then copies the frame the C Indicator is changed to an S

symbol

The received value of the Control Indicators for every frame

received is reported at the MAC Indicate Interface on sig-

nals MID(7 – 0) On a frame transmitted by this station the

returning Control Indicators give the transmission status

The Ending Delimiter followed by the Frame Status Indica-

tors should begin and end on byte boundaries Control Indi-

cators are repeated until the first non R S or T is received

The processing of properly aligned E A and C indicators by

the Ring Engine is detailed in Table 5-5 Given the shown

received Control Indicator values and the settings of the

internal flags the noted control indicator values will be

transmitted

TABLE 5-5 Control Indicators Processing

Received Indicators

Flags

Transmitted Indicators

Copy

XXX

110

XXX

110

111

XXX

Flag is set when the local FCS check fails or when the E Indicator is received as anything other than R

Flag is the internal

Flag or the external A Flag (pin EA) when OptionEmind is set

The Copy Flag is a one cycle delayed version of the VCOPY input

Flag indicates that an NSA frame is being received This signal is sampled at the same time that the received A indicator is being investigated

X Represents a Don’t Care Condition

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