DP83959 datasheet(16/38 Pages) NSC

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5.0

Functional Description (Continued)

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Optionally, conﬁguration information can be loaded into the

device at reset from values set by pull-up and/or pull-down

resistors on the D[3:0] and RA[4:0] pins. See Section 5.12

for more details.

The rising edge of the selected reset signal is used to start

the 1 second LED test operation.

As a power-on test feature, the DP83959 will assert all sin-

gle ended LED outputs, the DP83955/6 compatible LED

outputs and the 'B' outputs of the bi-color LED outputs. The

direct drive LED outputs are asserted during reset as well as

for 1 second following the trailing edge of reset, whereas the

DP83955/6 compatible LEDs will only be asserted for the 1

second test, not during reset. See the pin descriptions for

the LEDs in Section 4.3 for more details.

5.10

TRAFFIC MONITOR LED INTERFACE

The Network Trafﬁc Level Monitor function displays the net-

work utilization as a percentage on 8 LEDs connected in

bargraph format. LEDs connected to the /TRAF[1:8] outputs

will indicate the following network trafﬁc levels 1%, 2%, 3%,

6%, 12%, 25%, 50%, and >80% respectfully. These are cho-

sen in order to provide for an ergonomic display.

The Network Trafﬁc Level Monitor function uses a sum of the

internal carrier sense signals from each of the ports to as-

sess the amount of repeater activity in any given sample pe-

riod. Network activity is sampled at 6.25Hz. The activity

level is decoded into a percentage of the theoretical maxi-

mum and output to the /TRAF[1:8] pins for display on the

bargraph style LEDs. That is, all LED outputs up to and in-

cluding the currently determined network trafﬁc LED level

will be asserted. Figure 5 shows how to connect the trafﬁc

LEDs.

Additionally, three global LEDs are provided:

An Alert LED output indicates when trafﬁc level exceeds

80% for 1 second or more or when any of the eight

10BASE-T ports is partitioned for 1 second or more. The

output will remain active until the excess trafﬁc or long par-

tition event ends or for a minimum of 30ms (nominal value)

to ensure LED visibility.

A global activity LED output (/GACT) indicates the presence

of any receive activity, while a global collision LED output

(/GCOL) indicates the presence of collisions on any port.

These LED outputs have the capability to lengthen the time

the LED is active. At the end of each event, the output is held

asserted for 30 ms, or until another such event occurs.Thus,

at low levels of network activity (for /GACT) or network colli-

sions (for /GCOL), the LED is lit long enough to make it dis-

cernible to the human eye. At higher rates of events, the

relative brightness of the LEDs indicate high or low activity.

Figure 4.

DP83959 Reset Logic

Internal Power-On Reset

Pulse Generator

RES_INT/EXT

/MLOAD

Internal Reset

Signal

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