SPRADN4 December 2024 AM62P , AM62P-Q1
The series resistor on the clock output is required to resolve issues with signal distortion at the source of the clock signal because the clock output is also used for retiming. For MMCx interface an unbonded pad is used, so the series resistor is not a requirement for loopback. In some cases, a low value series resistor is needed for EMI / EMC purpose (reduce radiated emissions). The recommendation is to keep the series resistor as a place holder just in case the resistor is needed for improving signal integrity.