DP83241 datasheet(12/20 Pages) NSC

12 / 20 page

50 Detailed Information (Continued)

TABLE 5-1 Special External Components

Crystal Resonator

Part

C5410N

Manufacturer

NEL

Key Specifications

125000 MHz Center Frequency

20 PPM Accuracy 0 Cto a70 C

15 pF Load Capacitance

Varactor Diode

Part

MV2105

Manufacturer

Motorola

Key Specifications

Cap Tolerance g10%

VHF NPN Transistor

Part

PN3563

Manufacturer

National Semiconductor

Key Specifications

Inductor

Part

Manufacturer

Key Specifications

Turns

52 CONCENTRATOR AND DUAL ATTACH STATION

CONFIGURATIONS

521 Concentrator Applications

An application where many of the features of the CDD de-

vice are used is a FDDI concentrator A concentrator is

used to connect several workstations and peripherals to a

single node in the network A concentrator provides the abil-

ity to easily bypass or insert multiple stations into the net-

work The CDD device in each station is driven from a com-

mon oscillator instead of each CDD device being driven by

its own crystal In a small concentrator the same LBC

phase can be used in each station since the data flight time

from one board to another is small compared to the LBC

period and the skew between the CDD devices on the two

boards is minimal In a larger concentrator configuration

where this skew becomes too large the data setup time of

the downstream station will be directly impacted One way

to avoid this problem is to latch data into the next station

The strobe for the latch will be supplied by one of the LBC

outputs from the upstream station’s CDD device An LBC

output phase is chosen that occurs after the physical layer

data is stable Assuming that the data and LBC flight times

are equal the LBC output will latch data for the next station

The LBC output phase should be selected to give the opti-

mum setup and hold time for the receiving station’s physical

layer function

TLF10385 – 8

FIGURE 5-3 Small Concentrator Application

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