DP83256 datasheet(36/146 Pages) TI1

36 / 146 page

40 Modes of Operation (Continued)

45 CASCADE MODE

The PLAYERa device can operate in the Cascade (paral-

lel) mode

(Figure 4-5) which is used in high bandwidth

point-to-point data transfer applications This is a non-FDDI

mode of operation This is only available on the DP83257

device

Concepts

In the Cascade mode multiple PLAYERa devices are con-

nected together to provide data transfer at multiples of the

FDDI data rate Two cascaded PLAYERa devices provide

a data rate twice the FDDI data rate three cascaded

PLAYERa devices provide a data rate three times the FDDI

data rate etc

Multiple data streams are transmitted in parallel over each

pair of cascaded PLAYERa devices All data streams start

simultaneously and begin with the JK symbol pair on each

PLAYERa device

Data is synchronized at the receiver of each PLAYERa de-

vice by the JK symbol pair Upon receiving a JK symbol pair

a PLAYERa device asserts the Cascade Ready signal to

indicate the beginning of data reception

The Cascade Ready signals of all PLAYERa devices are

open drain ANDed together to create the Cascade Start

signal The Cascade Start signal is used as the input to

indicate that all PLAYERa devices have received the JK

symbol pair Data is now being received at every PLAYERa

device

and

can

transferred

from

the

cascaded

PLAYERa devices to the host system

See

Figure 4-6 for more information

Operating Rules

When the PLAYERa device is operating in Cascade mode

the following rules apply

1 Data integrity can be guaranteed if the worst case PMD

transmission skew between parallel media is less than

40 ns For example this amounts to about 785 meters of

fiber optic cable assuming a 1% worst case variance

2 Even though this is a non-FDDI application the general

rules for FDDI frames must be obeyed

Data frames must be a minimum of three bytes long

(including the JK symbol pair) Smaller frames will

cause Elasticity Buffer errors

Data frames must have a maximum size of 4500 bytes

with a JK starting delimiter and a T or R or S ending

delimiter

3 Due to the different clock rates the JK symbol pair may

arrive at different times at each PLAYERa device The

total skew between the fastest and slowest cascaded

PLAYERa devices receiving the JK starting delimiter

must not exceed 80 ns

4 The first PLAYERa device to receive a JK symbol pair

will present it to the host system and release the Cas-

cade Ready signal The PLAYERa device will present

one more JK as it waits for the other PLAYERa devices

to recognize their JK The maximum number of consecu-

tive JKs that can be presented to the host is 2

5 The Cascade Start signal is set to 1 when all the cascad-

ed PLAYERa devices release their Cascade Ready sig-

nals

6 Bit 4 (CSE) of the Receive Condition Register B (RCRB)

is set to 1 if the Cascade Start signal (CS) is not set

before the second falling edge of clock signal LBC from

when Cascade Ready (CR) was released CS has to be

set approximately within 80 ns of CR release This condi-

tion signifies that not all cascaded PLAYERa devices

have received their respective JK symbol pair with the

allowed skew range

7 PLAYERa devices may not report a Cascaded Synchro-

nization Error if the JK symbols are corrupted in the point-

to-point links

8 To guarantee integrity of the interframe information the

user must put at least 8 Idle symbol pairs between

frames The PLAYERa device will function properly with

only 4 Idle symbol pairs however the interframe symbols

may be corrupted with random non-JK symbols

The MACSI device could be used to provide the required

framing and optional FCS support

DP83256 Datasheet(PDF) 36 Page - Texas Instruments

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