HDMI 2.1¶

LattePanda Mu Ultra x86 compute module derives up to 3 HDMI outputs from the TCP0, TCP1, and TCP2 ports, supporting up to 4K @ 60Hz.

Display Capabilities

LattePanda Mu Ultra supports up to 3 independent displays, each capable of running up to 4K@60Hz concurrently.

Port Configuration¶

HDMI signals (operating in TMDS mode) can only be configured from TCP0, TCP1, or TCP2.

TCP2 corresponds to the DDIB on the LattePanda Mu — same pin positions, same function.
The default BIOS firmware enables TCP2 as HDMI. TCP0 and TCP1 are configured as USB Type-C ports by default.
Support for up to three HDMI outputs describes the hardware capability, not the default firmware configuration. Configuring TCP0 or TCP1 for HDMI (TMDS mode) requires customized BIOS firmware and changes the default function of the corresponding port.

Design Guidelines¶

Pin Definition¶

Port Name	Pin Number
TCP0 (TMDS Differential Pair)	227, 229, 233, 235, 239, 241, 245, 247
TCP0 DDC & HPD	177, 179, 187
TCP1 (TMDS Differential Pair)	220, 222, 226, 228, 232, 234, 238, 240
TCP1 DDC & HPD	173, 175, 185
TCP2 (TMDS Differential Pair)	197, 199, 203, 205, 209, 211, 215, 217
TCP2 DDC & HPD	169, 171, 183

AC Coupling & Pull-down Bias¶

Note

On LattePanda Mu Ultra compute module, TCP0, TCP1 and TCP2 signal lines do not integrate AC coupling capacitors.

Intel's reference design requires a specific AC Coupling + Pull-down Bias topology.

AC Coupling: A 100nF (0.1uF) capacitor must be placed in series on all four TMDS differential pairs. 0402 or smaller package is recommended to minimize parasitics.
Pull-down Bias: After the capacitor (connector side), each TMDS signal line must be pulled down to GND via a 470Ω resistor.
Switch Control: The ground connection of all 470Ω resistors should be gathered and controlled by an NMOS. The NMOS turns ON (enabling the pull-downs) ONLY when the system is in the working (S0) state and sleep/suspend (modern standby) state.

Why are 470Ω pull-down resistors mandatory?

This is the standard design required by Intel. Omitting the 470Ω resistor will cause the signal eye diagram to fail and lead to compatibility issues.

Polarity Check¶

HDMI TMDS differential pairs do not support polarity inversion.

Strict polarity matching must be implemented on the carrier board. Ensure that Positive (+) maps to Positive (+) and Negative (-) maps to Negative (-), as illustrated in the figure below.

+---------------------+                            +---------------------+
|  Compute Module     |                            |   HDMI Connector    |
|                     |                            |                     |
|  [TMDS_DATA_P] (+) >O===========================>O  [TMDS_DATA_P] (+)  |
|                     |                            |                     |
|  [TMDS_DATA_N] (-) >O===========================>O  [TMDS_DATA_N] (-)  |
|                     |                            |                     |
+---------------------+                            +---------------------+
          ^                                                   ^
          |                                                   |
          +----------- STRICT 1:1 MAPPING REQUIRED -----------+
                        Do NOT Swap P & N Signals

(The diagram above emphasizes polarity; therefore, AC coupling capacitors and pull-down resistors are omitted.)

Level Shifter¶

DDC (I2C) and HPD signals from compute module are 3.3V.
HDMI standard requires 5V logic levels.
Direct connection is prohibited. A level shifting circuit (using NMOS or dedicated chips) must be implemented on the carrier board.

No AUX Signal¶

When operating in TMDS mode, the AUX signals are unused, so they should be left not connected.

For example, when TCP2 is operating in TMDS mode, the following pins should be NC.

Pin 191: TCP2_AUX_N 
Pin 193: TCP2_AUX_P

Power Backflow Prevention¶

A diode must be connected in series between the system power and the 5V pin of the HDMI connector to prevent power conflict between the host and the device. This diode cannot be omitted. As shown below, this diode is D4.

However, the resettable fuse (F1, as shown below) is optional if space is limited.

Pull-Down for Unused HPD¶

The HPD pin of an unused video port must be pulled down to GND through a 100kΩ resistor to prevent a floating HPD input and false display detection. Use a separate resistor for each HPD pin.

For example, with the default BIOS firmware, TCP2 is configured for HDMI (TMDS) output. If TCP0 and TCP1 are not used for video output, pull down TCP0_HPD (pin 187) and TCP1_HPD (pin 185) to GND through individual 100kΩ resistors.

ESD Protection¶

Since HDMI ports are subject to frequent hot-plugging, they are vulnerable to Electrostatic Discharge (ESD). And TMDS signals are extremely sensitive to capacitance. So Ultra-low capacitance ESD protection diodes are mandatory.

Signal Type	Recommended Specs
High Speed (TMDS)	Junction Capacitance: < 0.18 pF Reverse Working Voltage: 3.3 V
Low Speed (DDC/HPD)	Junction Capacitance: < 3 pF Reverse Working Voltage: 5.5V or 6 V

Layout Guidelines¶

Parameter	Requirement
Differential Impedance	100Ω
Intra-pair Skew	< 5 mil
Inter-pair Skew	< 13 mm
AC Cap for TMDS	100nF nominal
Bias Resistor for TMDS	470Ω nominal
AC Cap & Bias Resistor Placement	As close to HDMI connector as possible (<13 mm)
Reference Plane	Continuous GND Recommended

Spacing & Crosstalk¶

Trace Type: Microstrip Differential Pair
Recommended Pair-to-Pair Spacing: ≥ 5W (where W is trace width).

To ensure signal integrity for HDMI 2.1 (4K@60Hz), a spacing of at least 5W is required to strictly minimize crosstalk.
Recommended General Spacing: Maintain at least 5W spacing between high-speed TMDS pairs and other signals (DDC, HPD, Power).
More details in High-Speed Interface Layout Guidelines