Schematic Review

[AdShea]

• Maybe add series resistors (10ohm?) to the transmit end of high-speed signals (SD card, RMII, I2S) to help reduce EMI and reflections on those signals.
• Add a Common-mode choke or ferrite beads to the audio jack on the DAC-side of the TVS diodes. (again, EMI. Also helps a bit with ESD/EFT too).
• Depending on what cap you're going to use for C2, you may run into issues with the 3.3V rail stability (look at Figure 15 and 16 of the LD39150DT33 datasheet). Electrolytic may be ok, ceramic will probably be unstable.
• Toss a footprint on there for an I2C EEPROM? No need to populate it now, but never know if there will be some "per-board-tuning" needs that you don't want to worry about dealing with on the SD-card.

I'll keep poking into datasheets, but here's a start.

[KyleCardoza]

Thank you for that.

[KyleCardoza]

All but the I2C EEPROM are now in the schematic. I'm curious what the benefit of the I2C EEPROM might be over flashing to the EZ80F91's on-chip ROM from the SD card.

[AdShea]

On chip ROM would work too. I'm guessing there's some way to clear from an external tool as well?

[KyleCardoza]

Using the ZDI port, and an ESP-based adapter designed by the AGON project, it's possible to flash the EZ80 chip directly, yes.