DP83850C datasheet(12/37 Pages) NSC

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3.0 Functional Description (Continued)

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3.9 Management Bus

The task of network statistics gathering in a repeater sys-

tem is divided between the DP83850C and DP83856

devices. Together, these devices collect all the required

management information (compliant to IEEE 802.3u clause

30) associated with a packet.

Each time a packet is received by a DP83850C, it drives

the device and the port number onto the management bus

in 3 contiguous nibbles of data.

During a single reception, only one DP83850C drives this

information onto the management bus. During a collision,

the management bus will TRI-STATE (because the infor-

mation on this bus becomes invalid).

The ﬁrst nibble of management data contains the least sig-

niﬁcant 4 bits of the RID number, the second contains the

most signiﬁcant bit of the RID number and the third con-

tains the number of the receiving port.

When the 100RIC is not receiving a packet, it monitors the

RID numbers from other 100RICs.

If there is a match

between any of these numbers and 100RIC’s own RID,

then a RID contention error signal (RID_ER) is asserted.

The management bus also indicates whether an elasticity

buffer error (due to under-run or over-run) has occurred by

asserting the /M_ER signal.

3.10 Management Event Flags and Counters

Repeater management statistics are supported either

directly by using the DP83850C's on-chip event ﬂags and

counters, or indirectly, by the DP83850C providing the

information to the DP83856 via the management and

transmit bus.

Management

information

maintained

within

the

DP83850C in two ways: event ﬂags and counters.

3.10.1 Event Flags

These are the events that provide a snapshot of the opera-

tion of the DP83850C. These events include:

s Auto-Partition State, indicating whether a port is current-

ly partitioned.

s Jabber State, indicating whether a port is in jabber state.

s Administration State, indicating if a port is disabled.

3.10.2 Event Counters

The event counters maintain the statistics for events that

occur too frequently for polled ﬂags, or are collision ori-

ented. Each port has its own set of event counters that

keep track of the following events:

s Port Collisions. A 32-bit counter providing the number of

collision occurrences on a port.

s Port Partitions. A 16-bit counter indicating the number of

times that the port has partitioned.

s Late Events. A 32-bit counter indicating the number of

times that a collision took place after 512 bit times (nom-

inal). In the case of late events, both the late event and

the collision counters will be incremented.

s Short Events. A 32-bits wide counter indicating the num-

ber of packets whose length is 76 bits (nominal) or less.

3.11 Serial Register Interface

The DP83850C has 64 registers held in two pages of 32

(Register Page 0 and Register Page 1). The registers are

16 bits wide. Only one page of registers can be accessed

at a time.

After power-up and/or reset, the DP83850C defaults to

ing 0001h to the PAGE register in Register Page 0, where-

upon further accesses will be to Register Page 1.

Figure 2. RID to /IR_VECT Mapping

Activity on the 100RIC

with RID=00010

Activity on the 100RIC

with RID=00011

/IR_Vect value on

the backplane

Activity on the 100RIC

with RID=00011

/IR_VECT value on

the backplane

Activity on the 100RIC

with RID=00010

RID=00010

RID=00011

00010

00011

00010

RID=00011

RID=00010

00010

00011

One port left

Collision

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