DP83261AVF datasheet(91/132 Pages) NSC

91 / 132 page

70 Signal Descriptions (Continued)

74 MAC REQUEST INTERFACE

The MAC Request Interface is used to gain access to the ring and to transmit data into the ring After a Request is submitted to

the interface the Ring Engine awaits for an appropriate Service Opportunity in which to service the Request Frames associated

with the Request are transmitted during an appropriate Service Opportunity Sections 52 and 53 provide important information

related to the functional operation of the interface

In the following sections an overview (Section 741) and detailed signal description (Section 742) are provided The detailed

description includes a signal by signal description followed by a state diagram that details the operation of the handshaking

signals Finally several example timing scenarios are shown (Section 743)

741 Overview

The MAC Request Interface signals provide the Request and Frame level handshakes required to transmit frames

The MAC Request Interface is divided into one group of data signals and four groups of control signals

The data signals consist of the 8 bits of MAC Request data with optional parity

The control signals consist of

Handshake signals that implement a Request level and Frame level handshake The state machines that specify the

interface handshake are provided and described in detail in Section 743

Service Parameters that convey the requested type of Service Opportunity

Frame Options that convey the special transmission options These are especially useful for MAC level bridging applica-

tions

Transmission Status that report the success andor failure of the transmission

742 Signals

Request Data

The MRD7 – 0 signals change on the rising edge of the Local Byte Clock signal (provided by the Clock Distribution Device)

Symbol

Description

MRP

MAC Request Parity

Odd parity on MRD7 – 0

MRD7–0

42–49

MAC Request Data

Data byte conveyed for transmission while the Transmit Acknowledge (TXACK)

signal is asserted

DP83261AVF Datasheet(PDF) 91 Page - National Semiconductor (TI)