DP83261 datasheet(75/132 Pages) NSC

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70 Signal Descriptions (Continued)

73 MAC INDICATION INTERFACE

The MAC Indication Interface provides a delayed version of the byte stream presented to the Ring Engine at the PHY Indication

Interface Every byte of all incoming frames is presented at the MAC Indication Interface Every byte time (80 ns) one byte of

data with Odd parity is presented at the MAC Indication Interface This byte stream is interpreted by the system interface logic

using the control signals that are provided in parallel with the byte stream These control signals are used to determine frame

boundaries in the byte stream determine whether or not to (continue to) copy a frame and to provide status on received PDUs

In the following sections an overview of the signals is provided (Section 731) as well as a detailed explanation (Section 732)

with several example timing scenarios (Section 733)

731 Overview

The MAC Indication Interface is divided into one group of data signals and five groups of control signals

The data signals consist of the 8 bits of MAC Indicate Data (MID) with parity

The control signals consist of 5 groups

PDU Sequencing to aid in delimiting PDUs from the byte stream and sequencing through fields in the received PDUs

PDU Flags to aid in the decision of whether or not to continue to copy a PDU

Termination Event to determine when and how a PDU terminated

Termination Status to provide status on received frames

External Flags to allow external address comparison and copy information to be conveyed back to the Ring Engine

The PDU Sequencing signals are asserted at different points within a PDU

RCSTART when the Starting Delimiter is present on MID

FCRCVD

when the Frame Control Field is on MID

DARCVD

when the last byte of the DA is on MID until the next Starting Delimiter

SARCVD

when the last byte of the SA is on MID until the next Starting Delimiter

INFORCVD when the fourth byte of the info field is on MID until the next Starting Delimiter

Not all of the sequencing signals would be used in a typical implementation

The PDU Flags provide the input for potential copy criteria and status breakpoints The results of the comparisons between the

station’s long or short address and the frame’s source and destination addresses are provided in the AFLAG and MFLAG

signals The sequencing information is used to determine when this information is valid Since the Ring Engine is capable of

accomplishing four internal comparisons on any given frame two signals give the internal comparison that was accomplished

AFLAG

Internal DA Match There are actually four AFLAGs as determined by the two signals FCSLShortLong DAIG

IndividualGroup Valid with DARCVD

MFLAG

Internal SA Match There are actually two MFLAGs as determined by the values of FCSL Valid with SARCVD

SAMESA

SA same as in previous frame Valid with SARCVD on Non-MAC frames Can be used by external logic to batch

status or reduce the number of interrupts when multiple frames are received from the same station

SAMEINFO First four bytes of Info same as in previous frame Valid with INFORCVD on MAC frames Can be used to inhibit

copying of identical MAC frames

No temporary buffering is provided in the Ring Engine The system interface must provide this buffering while the decision is

made on whether or not to continue to copy the frame

Termination Event

One of these signals is asserted at the end of every PDU

EDRCVD

when the Ending Delimiter is on MID until the end of the Frame Status (typically asserted for two byte times)

TKRCVD

when the Ending Delimiter of a token is on MID

FRSTRP

when the first Idle byte of a stripped frame is on MID

FOERROR when the byte with the format error is on MID

MACRST

when a MACRST occurs or Ring Engine in Stop Mode

DP83261 Datasheet(PDF) 75 Page - National Semiconductor (TI)

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