+5V Power Signal

[dnotq]

Starting a new issue since the "source not detected" issue was closed.

While the fix does provide +5V, it does not follow the specification. Some of the key statements are:

• "All Sources shall assert +5V Power signal whenever the Source is using the DDC or TMDS signals. The voltage driven by the Source shall be within the limits of 4.8V to 5.3V. A Source shall have +5V Power signal over-current protection of no more than 0.5A."

• "All Sources shall be able to supply a minimum of 55mA to the +5V Power pin. A Sink shall not draw more than 50mA of current from the +5V Power pin. When the Sink is powered on, it can draw no more than 10mA of current from the +5V Power signal."

• "The return for the +5V Power signal is DDC/CEC Ground signal."

The ground return for the +5V is very important, and it should never be assumed that they are all "tied together". Video signal returns need special attention, and should not be arbitrarily tied to something like the +5V return.

The current limiter is important in case a Sink or cable is faulty; protects the board and the vintage computer. There are chips that handle all of this, or you can roll your own +5V supply for the interface.

Even DVI 1.0 has a +5V requirement:

"2.2.6. DDC
2.2.6.1. System DDC Requirements

DDC2B support is required. The DDC +5 volt signal is required in a DVI compliant system.

Note: The power pin must be able to supply a minimum of 55 mA and the monitor may not draw more than 50 mA."

I would discourage just tying the Power pin to the board's +5V rail.