AM79C985JC datasheet(19/48 Pages) AMD

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Am79C985

PRELIMINARY

Network Activity Display

The eIMR+ status port can drive up to eight LEDs to in-

dicate the network-utilization level as a percentage of

bandwidth. The status port uses eight dedicated out-

puts (ACT0-7) to drive a series of LEDs. The number of

LEDs in the series that will be lit increases as the

amount of network activity increases. ACT0 represents

the lowest level of activity; ACT7 represents the high-

est. ACT0-7 are open-drain outputs that typically sink

12 mA of current to turn on the LEDs. See Figure 2.

Table 3 shows ACT0-7 as a function of the percentage

of network utilization. The table uses a scale that is

more sensitive at low utilization levels. 100% utilization

represents the maximum number of events that could

occur in a given window of time.

The update rate and corresponding internal sampling

window for ACT[7:0] is 250 ms. During this sampling

window, a counter is used to count the number of times

repeater transmit activity is TRUE. The counter uses a

free-running clock which has the granularity to detect

the minimum packet size of 96 bit times.

Figure 3 shows the timing relationship between the

sampling window, counting clock, and transmit activity.

Figure 2. Network Activity Display

Figure 3. Activity Sampling

Table 3. Network Utilization

Number of LEDs

Lit by ACT0-7

Percentage Utilization

>80%

>64%

>32%

>16%

>8%

>4%

>2%

>1%

ACT[0]

ACT[1]

ACT[4]

ACT[5]

ACT[2]

ACT[3]

ACT[6]

ACT[7]

eIMR+

LED

Interface

VDD

20651A-7

20651B-7

Sampling

Window

Counting

Clock

Xmit

Activity

counter is active

next counting cycle

latch data;

update display;

clear counter

20651B-8

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