DP83261AVF datasheet(5/132 Pages) NSC

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20 Architectural Description (Continued)

21 RING ENGINE

The BMAC device is operated by the Ring Engine which is

comprised of four blocks Receiver Transmitter MAC Pa-

rameter RAM and CountersTimers as shown in

Figure 2-2

211 Receiver

The Receiver Block accepts data from the PLAYER device

in the byte stream format (PH

Indicate)

Upon receiving the data the Receiver Block performs the

following functions

Determines the beginning and ending of a Protocol Data

Unit (PDU)

Decodes the Frame Control field to determine the PDU

type (frame or token)

Compares the received Destination and Source Address-

es with the internal addresses

Processes data within the frame

Calculates and checks the Frame Check Sequence at

the end of the frame

Checks the Frame Status field

And finally the Receiver Block presents the data to the

MAC Interface along with the appropriate control signals

(MA

Indicate)

212 Transmitter

The Transmitter Block inserts frames from this station into

the ring in accordance with the FDDI Timed Token MAC

protocol It also repeats frames from other stations in the

ring The Transmitter block multiplexes data from the MA

Request Interface and data from the Receiver Block During

Frame Transmission data from the Request Interface is se-

lected During Frame Repeating data from the Receiver

Block is selected

During Frame Transmission the Transmitter Block performs

the following functions

Captures a token to gain the right to transmit

Transmits one or more frames

Generates the Frame Check Sequence during transmis-

sion and appends it at the end of the frame

Generates the Frame Status field that is transmitted at

the end of the frame

Issues the token at the end of frame transmission

During Frame Repeating the Transmitter Block performs

the following functions

Repeats the received frame and modifies the Frame

Status field at the end of the frame as specified by the

standard

Whether transmitting or repeating frames the Transmitter

Block also performs the following functions

Strips the frame(s) that are transmitted by this station

Generates Idle symbols between frames

Data is presented from the Transmitter Block to the

PLAYER device in the byte stream format (PH

Request)

213 MAC Parameter RAM

The MAC Parameter RAM block is a dual port RAM that

contains MAC parameters such as the station’s short and

long addresses These parameters are initiallzed via the

Control Interface Both the Receiver and Transmitter Blocks

may access the RAM

TLF10387 – 4

FIGURE 2-2 Ring Engine Overview Block Diagram

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