AM79C987JC datasheet(19/30 Pages) AMD

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P R E L I M I N A R Y

Am79C987

Data Rate Mismatches

P[4:0] = 16–23, 31, R[4:0] = 10

Byte 0

Byte 1

Byte 2

Byte 3

bit 7

bit 31

bit 0

bit 24

MSB

LSB

D Port Read

“Data Rate Mismatches” is a read-only attribute that

counts the number of occurrences where the frequency,

or data rate of the incoming signal is detectably different

from the local transmit frequency. The attribute is a

32-bit counter that is incremented on each such event.

Note that the rate at which the “Data Rate Mismatches”

attribute will increment, will depend on the magnitude of

the difference between the received signal clock and the

local transmit frequency.

Auto Partitions

P[4:0] = 16–23, 31, R[4:0] = 11

Byte 0

Byte 1

Byte 2

Byte 3

bit 7

bit 31

bit 0

bit 24

MSB

LSB

D Port Read

“Auto Partitions” is a read-only attribute that counts the

number of instances where the repeater has partitioned

this port from the network. This attribute is a 32-bit

counter that is incremented on each such event. The ap-

proximate minimum time between counter roll-overs is

20 days.

Source Address Changes

P[4:0] = 16–23, 31, R[4:0] = 12

Byte 0

Byte 1

Byte 2

Byte 3

bit 7

bit 31

bit 0

bit 24

MSB

LSB

D Port Read

“Source Address Changes” is a read-only attribute that

counts the number of times the Source Address field of

valid frames received on a port changes. This attribute is

a 32-bit counter with a minimum rollover of 81 hours.

Note: This may indicate whether a port is connected to

a single DTE or another multi-user segment.

Last Source Address (LSA)

P[4:0] = 16–23, 31, R[4:0] = 14

Byte 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

bit 7

bit 31

bit 0

bit 24

MSB

LSB

D Port Read/Write

“Last Source Address” is a read/write attribute that

saves the value of the Source Address field of the last

valid frame it received. This attribute is a 6-byte field.

This 6-byte register may be read or written. This feature

allows the software to preset this attribute to the known

Node ID, for a single node segment. A change in the

contents of this register would then signal an anomaly.

This will cause the Source Address Changes attribute to

increment. Furthermore, setting the respective TP/AUI

Port Source Address Change Interrupt Enable bit (in the

Port Control Registers), can be used to generate a hard-

ware interrupt to signal the software to automatically

disable this port.

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