Specifications

DP83848Q-Q1
www.ti.com SNLS341C –MARCH 2011–REVISED MARCH 2015
The signal at the start of a packet is checked by the smart squelch and any pulses not exceeding the
squelch level (either positive or negative, depending upon polarity) will be rejected. Once this first squelch
level is overcome correctly, the opposite squelch level must then be exceeded within 150 ns. Finally the
signal must again exceed the original squelch level within 150 ns to ensure that the input waveform will
not be rejected. This checking procedure 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 the squelch level has not been generated for a time longer
than 150 ns, indicating 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.
Figure 5-9. 10BASE-T Twisted-Pair Smart Squelch Operation
5.5.1.3.3 Collision Detection and SQE
When in 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. Collisions are also reported when a
jabber condition is detected.
The COL signal remains set for the duration of the collision. If the PHY is receiving when a collision is
detected it is reported immediately (through the COL pin).
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 to indicate successful transmission. SQE is
reported as a pulse on the COL signal of the MII.
The SQE test is inhibited when the PHY is set in full duplex mode. SQE can also be inhibited by setting
the HEARTBEAT_DIS bit in the 10BTSCR register.
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