HDMI signals

Hot plug detect

HPD, Rsense and +5V, the three wires that start a link

Almost every HDMI problem that clears itself when you unplug and replug a cable is a hot plug detect problem. On the Diva you can produce that event from a browser.

Hot plug detect, usually shortened to HPD, is a single wire on pin 19 of every HDMI connector. The sink holds it high to say that it is present and that its EDID is ready to be read. When the line drops, the source treats the connection as gone and stops. It is the signal that starts and restarts everything else in the link.

Two other pins keep it company. Pin 18 carries +5V from the source, which powers the EDID memory inside the sink so that its capabilities can be read even when the display itself is in standby. Rsense, sometimes written RxSense, is the source noticing that the receiver has actually terminated the TMDS lines, which tells it that something at the far end is listening rather than merely plugged in. A source that sees +5V, a high HPD line and a readable EDID will attempt HDCP authentication and then send video.

The order matters because a source only re-reads the EDID when HPD goes low and comes back. Pulling that line down for a moment and releasing it is electrically the same as unplugging the cable and plugging it in again, which is why a hot plug event is the standard way of making a change take effect.

How the HDfury Diva uses hot plug detect

The Diva presents its own HPD and its own EDID to each of the four inputs rather than passing the display's straight through, which is what lets you change what a source is told without touching a cable. When you select a bank from the dropdown list of 100 tables in the EDID section there is nothing else to do: hot plug detect events reset the signal, so your chosen EDID is presented automatically.

When a source and a sink have failed to agree, the CONFIG section has ISSUE HOTPLUG, which sends a hotplug event and performs a soft reset of your setup. Try that before anything more drastic, such as a factory reset.

Autoswitching deliberately avoids these lines. AUTOSWITCH INPUTS in CONFIG watches the TMDS and pixel clock instead, because sources such as an ATV4K, an Xbox One X or a Shield keep sending +5V while in standby. Anything watching the +5V line would conclude they were still active and would never switch away from them.

When a hot plug is not enough

Some sources read an EDID once and then cache it. The Xbox One S and the Samsung K8500 are the two named in the manual: they may need their power cord removed and reconnected between EDID changes before they will look at the new EDID at all. If the change has clearly reached the Diva but the source is still sending the old format, the source is where to look.

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