DP83850C datasheet(11/37 Pages) NSC

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3.0 Functional Description (Continued)

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3.6 Jabber Protection State Machine

The jabber speciﬁcation for 100BASE-T is functionally dif-

ferent than 10BASE-T.

In 10BASE-T, each port's Jabber Protect State machine

ensures that Jabber transmissions are stopped after 5ms

and followed by 96 to 116 bit times silence before the port

is re-enabled.

In 100BASE-T, when a port jabbers, its receive and trans-

mit ports are cutoff until the jabber activity ceases. All other

ports remain unaffected and continue normal operation.

The 100BASE-T Jabber Protect Limit (that is, the time for

which a port can jabber until it is cutoff) for the DP83850C

is reached if the CRS is active for more than 655

µs.

A jabbering port that is cut off will be re-enabled when the

jabber activity ceases and the IDLE line condition is

sensed.

3.7 Auto-Partition State Machine

In order to protect the network from a port that is experi-

encing excessive consecutive collisions, each port must

have its own auto-partition state machine.

A port with excessive consecutive collisions will be parti-

tioned after a programmed number of consecutive colli-

sions occur on that port.

Transmitting ports will not be

affected.

The DP83850C has a conﬁguration bit that allows the user

to choose how many consecutive collisions a port should

experience before partitioning. This bit can be set for either

consecutive

collisions.

The

IEEE802.3u

100BASE-T standard speciﬁes the consecutive collisions

limit as greater than 60. A partitioned port will be recon-

nected when a collision-free packet of length 512 bits or

more (that is, at least a minimum sized packet) is transmit-

ted out of that port.

The DP83850C also provides a conﬁguration bit that dis-

ables the auto-partition function completely.

3.8 Inter Repeater Bus Interface

The Inter Repeater bus is used to connect multiple

DP83850Cs together to form a logical repeater unit and

also to allow a managed entity. The IR bus allows received

data

packets

transferred

from

the

receiving

DP83850C to the other DP83850Cs in the system. These

DP83850Cs then send the data stream to their transmit

enabled ports.

Notiﬁcation of collisions to other cascaded DP83850Cs is

as important as data transfer across the network. The arbi-

tration logic asynchronously determines if more than one

100RIC, cascaded together, are receiving simultaneously.

The IR bus has a set of status lines capable of conveying

collision information between DP83850Cs to ensure their

main state machines operate in the appropriate manner.

The IR bus consists of the following signals:

s Inter Repeater Data. This is the transfer data, in nibble

format, from the active DP83850C to all other cascaded

DP83850Cs.

s Inter Repeater Data Error. This signal carries the re-

ceive error status from the physical layer in real-time.

s Inter Repeater Data Valid. This signal is used to frame

good packets.

s Inter Repeater Data Clock. All IR data is synchronized

to this clock.

s Inter Repeater Data Outward Direction. This pin indi-

cates the direction of the data flow with respect to the

DP83850C. When the DP83850C is driving the IR bus

(i.e. it contains port N) this signal is HIGH and when the

DP83850C is receiving data from other DP83850Cs

over the IR bus this signal is LOW.

s Inter Repeater Bus Enable. This signal (connected to

the /ENABLE pin of the external transceivers on the IR

bus) is used in conjunction with the IRD_ODIR signal

(connected to the DIR pin of the transceivers) to TRI-

STATE these transceivers during the change of direction

from input to output, or vice versa. This signal is always

active allowing the IR bus signals to pass through the

transceivers into or out of the 100RIC. However when

the 100RIC switches from input mode (IRD_ODIR=0) to

output mode (IRD_ODIR=1), the /IR_BUS_EN signal is

deasserted allowing the transceivers to TRI-STATE dur-

ing the direction change. After this turn-around, this

signal is asserted back again. (IRD_ODIR assertion

(high) to /IR_BUS_EN low timing is a minimum of 0.1 ns.

and a maximum of 1.0. The time from /IR_BUS_EN

(high) to the IRD_ODIR high is a minimum of 10 ns. and

a maximum of 20 ns. In addition, /ACTIVEO assertion

(low) to /IR_BUS_EN high timing is a maximum of 1.0

ns.)

s Inter Repeater Activity. When there is network activity

the DP83850C asserts this output signal.

s Inter Repeater Collision Output. If there are multiple re-

ceptions on ports of a DP83850C or if the DP83850C

senses concurrent activity on another DP83850C it as-

serts this output.

s Inter Repeater Collision Input. This input indicates that

one of the cascaded DP83850Cs is experiencing a colli-

sion.

s Inter Repeater Vector. When there is reception on a port

the DP83850C drives a unique vector onto these lines.

The vector on the IR bus is compared with the Repeater

ID (RID). The DP83850C will continue to drive the IR

bus if both the vector and RID match.

The following ﬁgure shows the conditions that cause an

open collector vector signal to be asserted on the back-

plane bus.

Figure 1. Open Collector /IR_VECT[n]

As seen, if the RID[n]=1, and the repeater is receiving on a

port, then the /IR_VECT[n] value would be 1 due to the

pull-up on this pin. In the case that RID[n]=0, then a zero is

driven out on the /IR_VECT[n] signal.

As an example assume that two repeaters with RIDs equal

to RID #1=00010 and RID #2=00011 are connected

through the Inter-RIC bus. The following diagrams depict

the values of /IR_VECT signals over the backplane.

s Active Output. This signal is asserted by a DP83850C

when at least one of its ports is active. It is used to enable

external bus transceivers.

/IR_VECT[n]

RID[n]=0

/ACTIVEO=0

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