SNLS638A December 2018 – August 2019 DP83825I
The binary to MLT-3 conversion is accomplished by converting the serial binary data stream output from the NRZI encoder into two binary data streams with alternately phased logic one events. These two binary streams are then fed to the twisted-pair output driver which converts the voltage to current and alternately drives either side of the transmit transformer primary winding, resulting in a minimal current MLT-3 signal.
The 100BASE-TX MLT-3 signal sourced by the PMD output Pair common driver is controlled by the slew rate. The designer should consider this when selecting AC-coupling magnetics to ensure TP-PMD standard-compliant transition times (3 ns < Trise/fall < 5 ns).
The 100BASE-TX transmit TP-PMD function within the DP83825I is capable of sourcing only MLT-3-encoded data. Binary output from the PMD Output Pair is not possible in 100-Mbps mode. Fully-encoded MLT-3 on both Tx+ and Tx– and can be configured through Register 0x0404 (for example, in transformer-less designs).