I want to use BCM53128 IMP Port as RGMII to connect 88E1512 PHY.
According to 53128-DS07-R describe, RGMII support 2.5V/1.5V digital I/O, i have some questions.
1 : as 88E1512 describe, VDDO is for digital I/O, support 1.8V/2.5V/3.3V digital I/O, so here i must select 2.5V MODE, do it right?
2 : about the MDIO/MDC, as my understanding, MDIO should use 1.5K Res to pull up to 2.5V, does it right? But in the BCM953128R Reference Design, the MDIO use 4.7K to pull up to 3.3V(why in BCM953128R Reference Design pull up to 3.3, does it because OVDD tie to VCC3.3V?)
Please help me to conform it, thanks.
Please find the answer below per your two questions.
1. Right, select 2.5V mode.
2. BCM53128 MDC/MDIO pins are 3.3V I/O refer to OVDD2 3.3V I/O power rail. The OVDD I/O power rail is for IMP port interface only, it is not for MDC/MDIO. So in BCM953128R reference design, the MDIO is external pull up to 3.3V