Is dual screen HDMI to MIPI DSI adapter compatible with STM32?
Short answer: No, not directly. A dual screen HDMI to MIPI DSI adapter is designed to convert HDMI signals into MIPI DSI signals for driving displays, but STM32 microcontrollers (MCUs) lack the native hardware to output HDMI or handle the high-speed serial data that such adapters expect. However, with careful engineering and external components, limited compatibility can be achieved in specific scenarios. Let’s break this down with hard facts, data sheets, and real-world constraints.
The core issue lies in signal protocols. HDMI operates at multi-gigabit speeds (e.g., 1.65 Gbps per lane for 1080p at 60 Hz) using TMDS (Transition Minimized Differential Signaling). MIPI DSI, on the other hand, uses differential pairs with a D-PHY physical layer, typically running at 200 Mbps to 1.5 Gbps per lane. A dual screen HDMI to MIPI DSI adapter (like the one found at dual screen hdmi to mipi dsi adapter) includes a bridge chip (e.g., LT8918, TC358775, or SN65DSI86) that decodes HDMI and outputs MIPI DSI. These chips require an HDMI source—something STM32s cannot generate natively.
STM32 families, such as the STM32H7 series (e.g., STM32H743), have parallel RGB, LTDC (LCD-TFT Display Controller), and DSI Host interfaces, but no HDMI transmitter. The STM32MP1 series (cortex-A + M cores) includes a DSI Host, but still no HDMI output. To use a dual screen HDMI to MIPI DSI adapter, you would need to feed it an HDMI signal from an external source—like a Raspberry Pi, a camera module with HDMI out, or a dedicated HDMI encoder chip (e.g., ADV7511) driven by the STM32’s parallel RGB or DSI output. That adds complexity, cost, and latency.
Data point: The TC358775 bridge chip (commonly used in these adapters) requires a pixel clock between 25 MHz and 150 MHz, with HDMI input supporting up to 1080p@60Hz. STM32H7’s LTDC can generate pixel clocks up to 83 MHz (for 1280x720@60Hz), but the DSI Host on STM32H7 can output up to 1.5 Gbps per lane (4 lanes max). However, the HDMI output from an STM32 would need an external encoder like ADV7511, which adds $8-$15 in BOM cost and requires I2C configuration. Even then, the ADV7511 outputs standard HDMI, which the adapter can accept—but you are now using the adapter as a signal converter, not as a direct STM32 peripheral.
Real-world test: Engineers on the ST Community forum have attempted driving a dual screen HDMI to MIPI DSI adapter via an STM32F746 Discovery board’s LCD interface (parallel RGB) through an external HDMI encoder. Results showed frame rates dropping to 15-20 fps at 800x480 resolution due to bandwidth bottlenecks in the parallel-to-HDMI conversion. The adapter itself worked, but the STM32’s limited DMA bandwidth and lack of dedicated HDMI hardware caused tearing and sync issues. For dual screens, the adapter’s MIPI DSI output must drive two displays in a daisy-chain or dual-channel configuration—something STM32’s DSI Host can handle (e.g., STM32MP157 supports dual DSI lanes), but the adapter expects an HDMI input, not a direct DSI signal from the MCU.
Alternative approach: Some dual screen adapters have a configuration mode where they accept a parallel RGB input instead of HDMI, but this is rare. The dual screen HDMI to MIPI DSI adapter specifically lists HDMI input as mandatory. Checking the datasheet of the bridge chip (e.g., LT8918B) reveals that its input must be HDMI with TMDS levels (3.3V swing differential). STM32 GPIOs output 3.3V CMOS, not differential TMDS. You would need level shifters and a serializer—again, external components.
| Component | STM32 Capability | Adapter Requirement | Compatibility |
|---|---|---|---|
| Signal Protocol | Parallel RGB / DSI Host (up to 1.5 Gbps) | HDMI TMDS (up to 1.65 Gbps) | No direct match |
| Pixel Clock | Up to 83 MHz (H7 series) | 25-150 MHz | Possible with external encoder |
| Physical Layer | 3.3V CMOS / LVDS (DSI) | TMDS differential (3.3V swing) | Requires level translation |
| Power | 3.3V / 1.8V logic | 5V / 3.3V (adapter board) | Possible with regulator |
| Dual Screen Support | DSI dual lane (some models) | Dual MIPI DSI output | Adapter handles it, but input must be HDMI |
Bandwidth math: A 1080p@60Hz display requires ~3.2 Gbps bandwidth (24-bit color). HDMI 1.4 supports 10.2 Gbps. The adapter’s bridge chip can output dual MIPI DSI (4 lanes each) at up to 1.5 Gbps per lane, totaling 12 Gbps—enough for two 1080p screens. STM32H7’s DSI Host maxes out at 6 Gbps (4 lanes at 1.5 Gbps), which is insufficient for dual 1080p but fine for dual 720p. However, the adapter still needs an HDMI input, which STM32 cannot provide without an external chip. If you use an STM32MP157 with a DSI output, you could bypass the adapter entirely and drive MIPI DSI displays directly—but then you don’t need the adapter.
Latency and timing: The adapter introduces 1-2 frames of latency due to the bridge chip’s buffer and PLL locking. For real-time control applications (e.g., motor control with display feedback), this is problematic. STM32’s LTDC can achieve sub-frame latency (microseconds) when driving parallel RGB displays directly. Adding the adapter plus an HDMI encoder increases total latency to 16-33 ms at 60 Hz—noticeable in interactive systems.
Power consumption: The dual screen HDMI to MIPI DSI adapter draws 200-500 mA at 5V (depending on display load). STM32H7’s typical power budget is 300-500 mA at 3.3V. Adding the adapter doubles the system power draw. For battery-powered projects, this is a deal-breaker. The adapter also requires a separate 5V supply, while STM32 runs on 3.3V—adding a regulator adds heat and PCB space.
Firmware complexity: To use the adapter with an STM32, you must write drivers for the external HDMI encoder (e.g., ADV7511) over I2C, configure the bridge chip’s registers (via I2C or SPI), and synchronize the pixel clock. The adapter’s bridge chip often needs initialization sequences (e.g., setting DSI lane count, polarity, and video timings). Example: The TC358775 requires 40+ register writes to set up input and output modes. STM32’s HAL libraries don’t include these—you are on your own. Community projects (e.g., on GitHub) show that this takes 2-4 weeks of debugging for a single screen; dual screen adds complexity in synchronizing two DSI outputs.
Hardware modification needed: Some users have soldered wires directly to the adapter’s bridge chip to inject parallel RGB signals, bypassing the HDMI receiver. This voids warranty and requires understanding of the chip’s pinout (e.g., LT8918B has 128 pins). Even then, the chip expects a specific video timing (e.g., Hsync, Vsync, DE signals) that STM32’s LTDC can generate, but the voltage levels (1.8V vs 3.3V) may not match. Level shifters (e.g., TXS0108) add propagation delay of 4-6 ns, which can cause setup/hold violations at high pixel clocks.
Practical use cases where it works: If you use an STM32 as a co-processor to a main HDMI source (e.g., an FPGA or SoC that outputs HDMI), the adapter can drive dual MIPI DSI displays while the STM32 handles sensor data or user input via I2C/SPI. Example: A medical device with an STM32G4 for ADC readings and an FPGA generating HDMI for the adapter. Here, the STM32 is not the display driver—it’s a peripheral controller. The adapter’s compatibility with STM32 is indirect at best.
Alternative hardware: For dual MIPI DSI displays with STM32, consider the STM32MP157F-DK2 board, which has a native DSI connector supporting dual displays (via a DSI hub like SN65DSI86). This eliminates the need for an HDMI adapter. Cost: $79 for the board vs. $25 for the adapter plus $15 for an HDMI encoder. The MP1 also runs Linux, simplifying display drivers. If you must use an STM32H7, the LTDC can drive two parallel RGB displays with an external bridge like the SN65LVDS315 (LVDS to MIPI), but that’s a different path.
Reliability data: In a 2023 test by a display module vendor, the dual screen HDMI to MIPI DSI adapter showed a 98% success rate when used with standard HDMI sources (Raspberry Pi 4, Jetson Nano). When paired with an STM32H743 + ADV7511, the success rate dropped to 45% due to timing mismatches and clock jitter. The adapter’s bridge chip has a PLL that locks to the HDMI clock; if the STM32’s external oscillator has ±50 ppm tolerance, the PLL may lose lock, causing display flicker. STM32’s internal RC oscillator (up to ±1% accuracy) is unusable—you need an external 25 MHz crystal with ±25 ppm or better.
Pin compatibility: The adapter’s input is a standard HDMI Type A connector (19 pins). STM32 GPIOs cannot drive HDMI’s TMDS lines (which require 50-ohm impedance matching and differential signaling). You would need a HDMI transmitter chip like ADV7511 (which has 49-pin BGA package) or TFP410 (48-pin TQFP). These chips require careful PCB layout with controlled impedance traces (100 ohms differential). STM32 development boards (e.g., Nucleo-144) do not have such routing—you need a custom PCB.
Software stack: STM32CubeMX does not generate code for HDMI encoders or bridge chips. You must write bare-metal or HAL-based drivers for the encoder (I2C registers) and the adapter’s bridge chip (often via I2C or SPI). The bridge chip’s datasheet (e.g., TC358775XBG) is 200+ pages, with register maps for video timing, DSI configuration, and power management. Expect 500+ lines of C code just for initialization. For dual screen support, you need to configure the bridge chip’s dual DSI output mode—a feature that is poorly documented and often requires trial and error.
Market availability: As of 2025, no off-the-shelf dual screen HDMI to MIPI DSI adapter explicitly lists STM32 compatibility. Most are marketed for Raspberry Pi, BeagleBone, or FPGA boards with HDMI output. The dual screen HDMI to MIPI DSI adapter from DisplayModule (link above) is designed for single-board computers with HDMI ports. The product page mentions “input: HDMI,” not “input: parallel RGB or DSI from MCU.”
Cost breakdown: To make it work with STM32, add: ADV7511 ($12), 25 MHz crystal ($0.50), level shifters ($2), custom PCB ($50 for prototype), and 40 hours of engineering time ($2000 at $50/hr). Total: ~$2065 for a working prototype. Compare to using a Raspberry Pi 4 ($35) with the same adapter ($25)—total $60, plug and play. For most engineers, the STM32 path is not cost-effective unless you need the MCU’s specific peripherals (e.g., high-resolution ADC, CAN FD, or real-time control) and cannot use a Linux SBC.
Final technical note: The adapter’s MIPI DSI output uses a 15-pin FPC connector (0.3 mm pitch). STM32’s DSI Host uses a similar connector on some boards (e.g., STM32MP157F-DK2), but the pinout and voltage levels (1.8V vs 3.3V) may differ. Check the adapter’s datasheet: typical DSI voltage is 1.2V (D-PHY). STM32’s DSI PHY operates at 1.8V. A voltage mismatch can damage the adapter or the MCU. Use a level shifter like SN74AVC4T245 (4-bit, 1.2V to 1.8V) for each DSI data lane—that’s 4 shifters for a 4-lane DSI, adding $3 and PCB space.