DP83848MSQ National Semiconductor, DP83848MSQ Datasheet - Page 31

• Manufacturer Part Number: DP83848MSQ
• Manufacturer: National Semiconductor

Specifications of DP83848MSQ

• Lead Free Status / RoHS Status: Compliant

4.3.6 Jabber Function
The jabber function monitors the DP83848M'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 mod-
ule'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.
4.3.7 Automatic Link Polarity Detection and
Correction
The DP83848M's 10BASE-T transceiver module incorpo-
rates an automatic link polarity detection circuit. When
three consecutive inverted link pulses are received, bad
polarity is reported.
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.
The bad polarity condition is latched in the 10BTSCR reg-
ister. The DP83848M'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.
4.3.8 Transmit and Receive Filtering
External 10BASE-T filters are not required when using the
DP83848M, as the required signal conditioning is inte-
grated 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.
4.3.9 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 deasserts.
The last transition is always positive; it occurs at the cen-
ter 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.
4.3.10 Receiver
The decoder detects the end of a frame when no addi-
tional mid-bit transitions are detected. Within one and a
half bit times after the last bit, carrier sense is de-asserted.
Receive clock stays active for five more bit times after
CRS goes low, to guarantee the receive timings of the
controller.
31
www.national.com