Datasheet

DP83640
SNOSAY8E –SEPTEMBER 2007–REVISED APRIL 2013 www.ti.com
7.4.5 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 nominally 100 ns in duration and transmitted every 16 ms in the absence of transmit data.
Link pulses are 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 transmitter, receiver and collision
detection functions.
When the link integrity function is disabled (FORCE_LINK_10 of the 10BTSCR register), a good link is
forced and the 10BASE-T transceiver will operate regardless of the presence of link pulses.
7.4.6 Jabber Function
The jabber function monitors the DP83640's output and disables the transmitter if it attempts to transmit a
packet of longer than legal size. A jabber timer monitors the transmitter and disables the transmission if
the transmitter is active for approximately 85 ms.
Once disabled by the Jabber function, the transmitter stays disabled for the entire time that the ENDEC
module's internal transmit enable is asserted. This signal has to be de-asserted for approximately 500 ms
(the “unjab” time) before the Jabber function re-enables the transmit outputs.
The Jabber function is only relevant in 10BASE-T mode.
7.4.7 Automatic Link Polarity Detection and Correction
The DP83640's 10BASE-T transceiver module incorporates an automatic link polarity detection circuit.
When three consecutive inverted link pulses are received, bad polarity is reported. The bad polarity
condition is latched in the 10BTSCR register.
The DP83640's 10BASE-T transceiver module corrects for this error internally and will continue to decode
received data correctly. This eliminates the need to correct the wiring error immediately.
A polarity reversal can be caused by a wiring error at either end of the cable, usually at the Main
Distribution Frame (MDF) or patch panel in the wiring closet.
7.4.8 Transmit and Receive Filtering
External 10BASE-T filters are not required when using the DP83640, as the required signal conditioning is
integrated into the device.
Only isolation transformers and impedance matching resistors are required for the 10BASE-T transmit and
receive interface. The internal transmit filtering ensures that all the harmonics in the transmit signal are
attenuated by at least 30 dB.
7.4.9 Transmitter
The encoder begins operation when the Transmit Enable input (TX_EN) goes high and converts NRZ data
to pre-emphasized Manchester data for the transceiver. For the duration of TX_EN, the serialized
Transmit Data (TXD) is encoded for the transmit-driver pair (PMD Output Pair). TXD must be valid on the
rising edge of Transmit Clock (TX_CLK). Transmission ends when TX_EN de-asserts. The last transition
is always positive; it occurs at the center of the bit cell if the last bit is a one, or at the end of the bit cell if
the last bit is a zero.
7.4.10 Receiver
The decoder consists of a differential receiver and a PLL to separate a Manchester encoded data stream
into internal clock signals and data. The differential input must be externally terminated with a differential
100 Ω termination network to accommodate UTP cable.
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