Reducing the slew rate of MAC interface IOs can provide improvement in EMC emissions for some frequencies. This can be done using register 0x456.
0x456 bits [5] and [0] control the impedance of the RX and TX MAC interface pads, respectively, which impacts the slew rate. 0 is fast mode and 1 is slow mode. These are the only two options and bits[9:6] and [4:1] have no effect.
