DP83843 datasheet(23/87 Pages) NSC

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2.0 Functional Description (Continued)

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input waveform will not be rejected. The checking proce-

dure results in the loss of typically three preamble bits at

the beginning of each packet.

Only after all these conditions have been satisﬁed will a

control signal be generated to indicate to the remainder of

the circuitry that valid data is present. At this time, the

smart squelch circuitry is reset.

Valid data is considered to be present until squelch level

has not been generated for a time longer than 150ns, indi-

cating the End of Packet. Once good data has been

detected the squelch levels are reduced to minimize the

effect of noise causing premature End of Packet detection.

The receive squelch threshold level can be lowered for use

in longer cable applications. This is achieved by setting the

LS_SEL bit in the 10BTSCR (bit 6, register 18h). Collision

Detection

For Half Duplex, a 10BASE-T collision is detected when the

receive and transmit channels are active simultaneously.

Collisions are reported by the COL signal on the MII.

If the ENDEC is transmitting when a collision is detected,

the collision is not reported until seven bits have been

received while in the collision state. This prevents a colli-

sion being reported incorrectly due to noise on the network.

The COL signal remains set for the duration of the collision.

If the ENDEC is receiving when a collision is detected it is

reported immediately (through the COL).

When heartbeat is enabled, approximately 1

µs after the

transmission of each packet, a Signal Quality Error (SQE)

signal of approximately 10 bit times is generated (inter-

nally) to indicate successful transmission. SQE is reported

as a pulse on the COL signal of the MII.

2.4.4 Carrier Sense

Carrier Sense (CRS) may be asserted due to receive activ-

ity once valid data is detected via the smart squelch func-

tion.

For 10 Mb/s Half Duplex operation, CRS is asserted during

either packet transmission or reception.

For 10 Mb/s Full Duplex operation, CRS is asserted only

due to receive activity.

CRS is deasserted following an end of packet.

In Repeater mode, CRS is only asserted due to receive

activity.

2.4.5 Normal Link Pulse Detection/Generation

The link pulse generator produces pulses as deﬁned in the

IEEE 802.3 10BASE-T standard. Each link pulse is nomi-

nally 100 ns in duration and is transmitted every 16 ms

± 8

ms, in the absence of transmit data.

Link pulse is used to check the integrity of the connection

with the remote end. If valid link pulses are not received,

the link detector disables the 10BASE-T twisted pair trans-

mitter, receiver and collision detection functions.

When the link integrity function is disabled, the 10BASE-T

transceiver will operate regardless of the presence of link

pulses.

2.4.6 Jabber Function

The jabber function monitors the DP83843's output and

disables the transmitter if it attempts to transmit a packet of

longer than legal size. A jabber timer monitors the transmit-

ter and disables the transmission if the transmitter is active

for approximately 20-30 ms.

Once disabled by the Jabber function, the transmitter stays

disabled for the entire time that the ENDEC module's inter-

nal transmit enable is asserted. This signal has to be de-

asserted for approximately 400-600 ms (the “unjab” time)

before the Jabber function re-enables the transmit outputs.

The Jabber function is only meaningful in 10BASE-T mode.

2.4.7 Status Information

10BASE-T Status Information is available on the LED out-

put pins of the DP83843. Transmit activity, receive activity,

link status, link polarity and collision activity information is

output to the ﬁve LED output pins (LED_RX, LED_TX,

LED_LINK, LED_FDPOL, and LED_COL). Additionally, the

active high SPEED10 output will assert to indicate 10 Mb/s

operation.

If required, the LED outputs can be used to provide digital

status information to external circuitry.

The link LED output indicates good link status for both 10

and 100 Mb/s modes. In Half Duplex 10BASE-T mode,

LED_LINK indicates link status.

The link integrity function can be disabled. When disabled,

the transceiver will operate regardless of the presence of

link pulses and the link LED will stay asserted continuously.

2.4.8 Automatic Link Polarity Detection

The DP83843's 10BASE-T transceiver module incorpo-

rates an automatic link polarity detection circuit. When

seven consecutive link pulses or three consecutive receive

Figure 1. 10BASE-T Twisted Pair Smart Squelch Operation

<150ns <150ns

>150ns

start of packet

end of packet

Vsq +

Vsq -

Vsq +

reduced

Vsq -

reduced

Twisted Pair Squelch Operation

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