# Diode Mode Implementation Details

To implement diode mode on a microcontroller like the Raspberry Pi Pico, follow this circuit and logic.

## Circuit Design
1. **Pull-up Resistor**: Connect a 10kΩ resistor from 3.3V to the common Signal pin of your Multiplexer.
2. **Measurement Point**: Connect an ADC pin (e.g., GPIO 26) to the same Signal pin of the Multiplexer.
3. **HDMI Ground**: Connect HDMI Pin 17 (DDC/CEC Ground) and the Shell to the Microcontroller's Ground.

## Logic (Pseudo-code)
```cpp
float measureDiode(int channel) {
    // 1. Select the channel on the Mux
    setMuxChannel(channel);
    
    // 2. Wait for voltage to stabilize
    sleep_ms(5);
    
    // 3. Read ADC value (0-4095 for 12-bit ADC)
    uint16_t raw = adc_read();
    
    // 4. Convert to voltage
    float voltage = (raw * 3.3f) / 4095.0f;
    
    return voltage;
}
```

## Fault Logic for Intake Mode
The software uses the following logic to provide "Educated Guesses":

| Reading | Possible Fault | Hint |
|---------|----------------|------|
| 0.0V - 0.1V | Short to Ground | Check ESD protection diodes or internal IC short. |
| 1.0V - 3.2V | High Resistance / Open | Check for cracked solder joints on the HDMI port. |
| 3.3V (VCC) | Full Open | Line is completely disconnected. Port might be ripped. |
| 0.3V - 0.7V | Nominal | Line is likely connected to Redriver or APU correctly. |

## Redriver IC Testing
If all lines show nominal diode readings but there is still no video:
1. Check the **+5V line** (Pin 18). If it's missing, the console won't trigger the TV's HPD.
2. Check the **DDC lines** (SCL/SDA). If these are open, the console cannot read the EDID from the TV.
3. If Diode mode is perfect, the issue is likely the **Redriver IC** itself being powered down or having internal logic failure, or the **APU** encoder.