SLLA682 July   2025 TDP142

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Device Configuration
  6. 3Equalization Selection
  7. 4Equalization Selection Example
  8. 5AUXP/N and SNOOPENZ Configuration
  9. 6Layout Guidelines
    1. 6.1 GND Stitching
    2. 6.2 AC-Coupling Capacitors
    3. 6.3 Layout Example
  10. 7Summary
  11. 8References

5 AUXP/N and SNOOPENZ Configuration

TDP142 uses AUXp and AUXn pins to snoop AUX. AUX snooping enables TDP142 to monitor the native AUX traffic as the traffic traverses between DisplayPort source and DisplayPort sink. The TDP142 snoops native AUX writes to DisplayPort sink’s DPCD registers 0x00101 (LANE_COUNT_SET) and 0x00600 (SET_POWER_STATE). TDP142 disables/enables lanes based on value written to LANE_COUNT_SET. The TDP142 disables all lanes when SET_POWER_STATE is in the D3. Otherwise, active lanes is based on value of LANE_COUNT_SET.

In GPIO mode, AUX snooping is enabled by strapping SNOOPENZ pin low either pulling down to GND directly or to GND with 1k pull down resistor. In I2C mode, AUX snooping is enabled by default. AUX snooping can be disabled by writing 1 to bit 7 of the register 0x13.

When AUX snooping is disabled, all four DisplayPort lanes is active in GPIO mode. In I2C mode, each lane can be enabled or disabled by writing to bit [3:0] of the register 0x13.

AUXP needs to have a 100kΩ pull-down resistor and AUXN needs to have a 100kΩ pull-up resistor for the source. For sink, AUXp has 1M pullup to 3.3V and AUXn has 1M pulldown to GND. These resistors must be on the TDP142 side of the 100nF capacitors.

For the application supporting Dual mode DisplayPort: SNOOPENZ pin must be connected to the CONFIG1 on DisplayPort Receptacle through a buffer like the SN74AHC125. The buffer is needed because the internal pulldown on SNOOPENZ pin is too strong to register a valid VIH when a Dual mode adapter is plugged into the DisplayPort receptacle.