AM79C985 Advanced Micro Devices, AM79C985 Datasheet - Page 19

• Manufacturer Part Number: AM79C985
• Description: enhanced Integrated Multiport Repeater Plus (eIMR+)
• Manufacturer: Advanced Micro Devices

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 (ACT
LEDs in the series that will be lit increases as the
amount of network activity increases. ACT
the lowest level of activity; ACT
est. ACT
12 mA of current to turn on the LEDs. See Figure 2.
Table 3 shows ACT
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
.
0-7
0-7
are open-drain outputs that typically sink
) to drive a series of LEDs. The number of
0-7
as a function of the percentage
eIMR+
LED
Interface
Sampling
Counting
Window
Activity
ACT[0]
ACT[1]
ACT[2]
ACT[3]
ACT[4]
ACT[5]
ACT[6]
ACT[7]
7
Clock
Xmit
represents the high-
Figure 2. Network Activity Display
0
counter is active
Figure 3. Activity Sampling
P R E L I M I N A R Y
represents
Am79C985
latch data;
update display;
clear counter
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.
Number of LEDs
next counting cycle
Lit by ACT
8
7
6
5
4
3
2
1
Table 3. Network Utilization
0-7
V
20651A-7
DD
Percentage Utilization
>80%
>64%
>32%
>16%
>8%
>4%
>2%
>1%
20651B-7
20651B-8
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