DP83261AVF datasheet(4/132 Pages) NSC

4 / 132 page

20 Architectural Description

The BMAC device receivers transmits and strips or repeats

Protocol Data Units (PDUs ie

Tokens and Frames) and

handles the token management functions required by the

timed token protocol in accordance with the FDDI MAC

Standard

The BMAC device is comprised of the Ring Engine (RE) and

interfaces to the Control Bus (Control Interface)

the

PLAYER device (PHY Interface) and a System Interface

such as the BSI device (MAC Interface) as shown in

Figure 2-1

On transmission the system interface prepares one or more

frames for transmission and requests a service opportunity

Based on the requested service class and requested token

type the Ring Engine waits for a token meeting the request-

ed criteria When a token is captured the Ring Engine sig-

nals the interface and soon thereafter transmission begins

After traversing the ring frames are stripped based on the

Source Address Frames with a Source Address matching

one of the station individual addresses are stripped by the

Ring Engine Status is available at the MAC interface for

every transmitted frame

For reception the Ring Engine sequences through the in-

coming byte stream comparing received destination ad-

dresses against the station’s short or long address The re-

sults of these comparisons are made available at the MAC

interface The System Interface then decides how to handle

the frame In the normal case a frame with a Destination

Address matching one of the station addresses is copied

and passed to the system

The BMAC device utilizes a full duplex byte-wide (symbol

pair) architecture There are two bytes of delay in the Trans-

mit path three bytes of delay in Receive and Repeat paths

and two bytes of delay in the Loopback path

TLF10387 – 2

FIGURE 2-1 BMAC Device Interfaces

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