An HDMI connection starts with more than just video data. The source and display chain exchange status and capability information. If that process runs differently after standby, an input change or switching on a receiver, the picture may stay away or re-sync.

EDID and HPD

EDID tells the source what the chain supports. HPD (Hot Plug Detect) signals that the HDMI status has changed. The Dr HDMI can present a fixed EDID and generate an HPD event after a bank change, so the source reads the selected information again.

Diagnosis in a fixed order

  1. Test a simple chain.Connect source → Dr HDMI → display and temporarily remove the receiver, splitter or extender from the route.
  2. Start conservatively.Test bank 4 (720p), then bank 3 (1080i) and then bank 2 or 1.
  3. Copy the sink.If a direct picture works, copy the display EDID to bank 8.
  4. Rebuild the chain.Add components one at a time so you can see where the handshake changes.

What the handshake consists of

  1. +5V and Hot Plug Detect.The source puts 5 volts on the cable; the display answers via the HPD line that it is ready.
  2. Reading the EDID.The source reads over the Display Data Channel (DDC) which formats the chain supports.
  3. HDCP authentication.With protected content, source and display verify each other, also over DDC.
  4. Picture and sound.Then the TMDS signal follows in the selected format.

What Dr HDMI does in that process

Dr HDMI steps in at steps 1 and 2: it presents the selected EDID and triggers an HPD event after a bank change. It passes HDCP handshakes through unchanged. So if a source requires HDCP and the display does not support it, the picture stays away; an EDID manager does not solve that.

The Dr HDMI does not repair a faulty HDMI port and does not make insufficient cable bandwidth unlimited. It is mainly intended to make EDID/HPD behaviour controllable.