TMDS1204EVM: Optimal AC-Coupled Mode Setup & I2C Register Programming for Basic Sanity Testing

Hi everyone,

I'm working with the TMDS1204 HDMI redriver EVM and need guidance on setting it up in AC-coupled mode with I2C programming for basic sanity and stability testing. I want to pass a signal from a PC video source through to an HDMI sink/display for validation and oscilloscope probing.

Hardware Setup:

• PC HDMI output → TMDS1204 EVM input

• TMDS1204 EVM output → HDMI display (or breakout adapter for scope measurements)

• Using Aardvark I2CSPI host for register programming

Current Configuration Questions:

1. AC-Coupled Mode Setup: For sink-side applications, I believe I need:

   J27 jumper: Short 1 to 2 (AC_EN enabled)

   Ensure 100nF capacitors are populated on OUT_D[2:0] and OUT_CLK lanes

   499Ω pull-down resistors to ground after coupling caps

2. Essential I2C Register Programming:
   What's the minimal register configuration needed for reliable signal pass-through? Based on the datasheet, I'm thinking: 

   0x09, 0x00 // Exit power-down (PDEN = 0)
   0x0A, 0x00 // Enable rate and TXFFE snooping
   0x0D, 0xA3 // Linear mode, DC-coupled TX, 0dB DCG, 100Ω term
   0x0E, 0x97 // CTLE selection for HDMI 1.4/2.0/2.1
   0x11, 0x0F // Enable all four lanes

3. DDC/HPD Configuration:
   Should I enable the DDC level shifter (J31: short 2-3) and ensure proper HPD routing (populate R131, depopulate R129) for standard operation?

Specific Goals:

• Achieve basic video pass-through from PC to display

• Enable oscilloscope probing of TMDS lanes at output

• Maintain link stability for various HDMI modes (1.4/2.0/2.1) but primarily for HDMI 2.1

• Minimize register complexity while ensuring reliable operation

Questions:

• Are there any critical registers I'm missing for AC-coupled operation?

• What's the recommended approach for EQ settings in a sink application?

• Should I disable certain features (like AEQ) for initial testing?

• Any specific considerations for different HDMI data rates?
  
  

Any insights from those who've successfully configured the TMDS1204 in similar setups would be greatly appreciated!

Thanks in advance!