What is the pinout of a 3.4 inch transmissive TFT LCD?

If you are working with a 3.4 inch transmissive TFT LCD like the popular 3.4 inch 480x480 transmissive tft display, the pinout is the single most critical piece of hardware documentation you need to get the display talking to your microcontroller or single-board computer. For a typical 480x480 resolution panel using an SPI (Serial Peripheral Interface) plus RGB interface, the pinout consists of 50 pins on a 0.5mm pitch FPC connector. The first thing to know: this is not a simple 8-pin OLED. You are dealing with a hybrid interface that combines a high-speed serial bus for command and configuration with a parallel RGB bus for pixel data. The exact pinout can vary slightly between manufacturers, but for the DM-TFT34-486 model and most compatible 3.4 inch round or square panels, the pin assignments break down into five functional groups: power supply, backlight, SPI control, RGB data, and touch controller (if integrated). Let me walk through each group with specific pin numbers, voltage levels, and timing constraints that you will actually need when routing a PCB or wiring a breadboard prototype.

Power Supply Pins – The display module requires multiple voltage rails. Pin 1 and Pin 2 are typically VDD (2.8V to 3.3V) for the logic core. Do not feed 5V into these pins; the internal driver IC, usually an ILI9488 or ST7701S variant, will be damaged. Pin 3 and Pin 4 are VDDI (1.8V to 3.3V) for the I/O interface. If your microcontroller runs at 3.3V, tie VDDI to the same rail as VDD. Pin 5 and Pin 6 are GND. The backlight requires a separate supply: Pin 47 and Pin 48 are LED+ (anode) and Pin 49 and Pin 50 are LED- (cathode). The backlight forward voltage is typically 3.0V to 3.3V at 20mA per LED string. With 4 LEDs in parallel, the total backlight current draw is around 80mA. Do not exceed 100mA or you risk burning out the LEDs. Some modules include a backlight enable pin (BL_EN) on Pin 46, which expects a 3.3V logic high to turn on the backlight. If you skip this pin, the backlight stays off regardless of the LED power.

SPI Control Interface – The SPI bus handles register writes, gamma correction, and sleep mode commands. Pin 7 is CS (chip select, active low). Pin 8 is DCX (data/command control). A logic low on DCX means the next byte is a command; a logic high means it is data. Pin 9 is SDI (serial data input) also called MOSI. Pin 10 is SDO (serial data output) also called MISO – this is often unused in write-only configurations but can be used for reading register values. Pin 11 is SCK (serial clock). The maximum SPI clock frequency for this driver IC is 30MHz, but in practice, 10MHz to 20MHz works reliably with most STM32 or ESP32 microcontrollers. Pin 12 is RESET (active low). A 10ms low pulse after power-up is required to initialize the driver. If you tie RESET to the microcontroller reset line, the display will reset every time the MCU resets, which is usually fine. The SPI pins are 3.3V tolerant, but 5V logic will fry the driver IC. Use level shifters if your MCU runs at 5V.

RGB Parallel Data Interface – This is where the pixel data actually flows. The 3.4 inch 480x480 display uses an 18-bit RGB interface (6 bits per color), but the pinout provides 24 pins for RGB data (R0-R7, G0-G7, B0-B7). The extra two bits per color are simply not connected or grounded internally. Pin 13 to Pin 20 are the red data lines (R0 is LSB, R7 is MSB). Pin 21 to Pin 28 are green data lines. Pin 29 to Pin 36 are blue data lines. You need to connect all 24 pins even if only 18 are used, because leaving them floating can cause crosstalk and flickering. Pin 37 is DOTCLK (pixel clock). For a 480x480 display running at 60Hz refresh, the pixel clock frequency is approximately 480 * 480 * 60 * 1.2 (blanking overhead) = 16.6MHz. The actual recommended DOTCLK from the datasheet is 18MHz to 20MHz. Pin 38 is HSYNC (horizontal sync, active low). Pin 39 is VSYNC (vertical sync, active low). Pin 40 is DE (data enable). Some configurations use DE only without HSYNC/VSYNC, but the pinout still provides all three. Pin 41 is TE (tearing effect output) – this pin goes high when the display is in the vertical blanking period. You can use it for frame synchronization to avoid tearing. Pin 42 is NC (no connect) on most modules. The RGB interface timing requires a specific sequence: after VSYNC goes low for 1 to 10 lines, HSYNC pulses for each line. The DE signal must be high only during active pixel data. If you are using a microcontroller with a built-in LCD controller like the ESP32-S3, you can configure the timing registers directly. For a Raspberry Pi, you need to adjust the device tree overlay to match the 18-bit RGB666 mode.

Touch Controller Interface – Many 3.4 inch TFT modules include a capacitive touch panel with an FT6336 or similar controller. The touch interface uses I2C: Pin 43 is SDA (data), Pin 44 is SCL (clock), Pin 45 is INT (interrupt output, active low). The I2C address is usually 0x38 for the FT6336. The touch controller operates at 3.3V and draws about 5mA. The INT pin goes low when a touch is detected, and you can read the touch coordinates over I2C. The maximum I2C clock speed is 400kHz. Some modules also have a touch reset pin (RST) on Pin 46, but this is often shared with the display RESET. If you do not need touch, you can leave these pins unconnected, but make sure to pull the INT pin high with a 10k resistor to avoid floating inputs.

Pinout Table for DM-TFT34-486 (50-pin FPC)

Here is the exact pin mapping based on the production datasheet for the 3.4 inch 480x480 transmissive TFT display. Use this table as your reference when designing the PCB footprint.

Pin 1: VDD (2.8-3.3V)
Pin 2: VDD (2.8-3.3V)
Pin 3: VDDI (1.8-3.3V)
Pin 4: VDDI (1.8-3.3V)
Pin 5: GND
Pin 6: GND
Pin 7: CS (SPI chip select)
Pin 8: DCX (data/command)
Pin 9: SDI (SPI MOSI)
Pin 10: SDO (SPI MISO)
Pin 11: SCK (SPI clock)
Pin 12: RESET (active low)
Pin 13: R0 (red LSB)
Pin 14: R1
Pin 15: R2
Pin 16: R3
Pin 17: R4
Pin 18: R5
Pin 19: R6
Pin 20: R7 (red MSB)
Pin 21: G0 (green LSB)
Pin 22: G1
Pin 23: G2
Pin 24: G3
Pin 25: G4
Pin 26: G5
Pin 27: G6
Pin 28: G7 (green MSB)
Pin 29: B0 (blue LSB)
Pin 30: B1
Pin 31: B2
Pin 32: B3
Pin 33: B4
Pin 34: B5
Pin 35: B6
Pin 36: B7 (blue MSB)
Pin 37: DOTCLK (pixel clock)
Pin 38: HSYNC (horizontal sync)
Pin 39: VSYNC (vertical sync)
Pin 40: DE (data enable)
Pin 41: TE (tearing effect)
Pin 42: NC
Pin 43: SDA (touch I2C data)
Pin 44: SCL (touch I2C clock)
Pin 45: INT (touch interrupt)
Pin 46: BL_EN (backlight enable) or RST (touch reset)
Pin 47: LED+ (backlight anode)
Pin 48: LED+ (backlight anode)
Pin 49: LED- (backlight cathode)
Pin 50: LED- (backlight cathode)

Note: Pins 1 and 2 are internally connected, as are pins 3 and 4. You only need to connect one of each pair, but connecting both improves current handling. The same applies to the backlight pins 47-48 and 49-50.

Electrical Characteristics and Timing – The 3.4 inch transmissive TFT LCD draws about 120mA total with the backlight on and the display showing a full white pattern. The logic section draws 20mA, and the backlight draws 80mA to 100mA. The RGB interface voltage levels are 3.3V CMOS, meaning the logic high threshold is 2.0V minimum and the logic low threshold is 0.8V maximum. The rise and fall times for the RGB signals should be less than 5ns to avoid signal integrity issues. If you are using long wires (more than 10cm), add series resistors of 22 ohms on each RGB data line to dampen reflections. The SPI signals are less critical, but keep the clock line shorter than 15cm. The DOTCLK frequency of 18MHz means the pixel data rate is 18 million pixels per second. With 480x480 resolution, that gives a frame rate of 60Hz with a horizontal blanking period of 40 pixels and a vertical blanking period of 10 lines. The exact timing parameters from the driver IC datasheet: HBP (horizontal back porch) = 10 DOTCLK cycles, HFP (horizontal front porch) = 10 DOTCLK cycles, VBP (vertical back porch) = 2 lines, VFP (vertical front porch) = 2 lines. If you set these values incorrectly, the image will be shifted or distorted.

Common Wiring Mistakes – The most frequent error is mixing up the SPI and RGB pins. The CS pin is not the same as the chip select for the RGB interface. The DCX pin is often confused with the DE pin. DCX is for SPI command/data selection, while DE is for RGB data enable. Another mistake is connecting the backlight LED+ to 5V without a current-limiting resistor. The backlight LEDs have an internal resistor on some modules, but not all. Check the datasheet: if the module does not have a built-in resistor, you need to add a 10 ohm resistor in series with the LED+ line to limit current to 80mA. Also, never connect the touch controller pins to 5V logic. The FT6336 is strictly 3.3V. If you are using a 5V Arduino, use a level shifter for the I2C lines. The interrupt pin can be connected directly to a 5V input pin if the Arduino has 5V tolerant inputs, but the SDA and SCL lines must be level shifted.

Physical Dimensions and Connector – The 50-pin FPC connector has a 0.5mm pitch, meaning the center-to-center distance between pins is 0.5mm. The connector width is about 25mm. The FPC cable is usually 0.3mm thick. When you solder a FPC connector to your PCB, make sure the footprint matches the pinout exactly. The pin 1 marking is usually indicated by a small triangle or a dot on the FPC. Double-check the orientation: the metal contacts on the FPC should face down when inserted into the connector. Some modules use a ZIF (zero insertion force) connector, which has a flip-up latch. Do not force the FPC in without lifting the latch. The connector part number is typically FH12-50S-0.5SH or equivalent. You can also use a 50-pin 0.5mm pitch FPC breakout board if you are prototyping on a breadboard, but be aware that the breadboard will introduce parasitic capacitance that can degrade the RGB signals above 10MHz.

Software Configuration – After wiring the pinout correctly, you need to initialize the driver IC via SPI. The initialization sequence for the ST7701S or ILI9488 includes commands like: software reset (0x01), sleep out (0x11), display on (0x29), and gamma curve settings. The exact sequence is about 30 commands long. For the 3.4 inch 480x480 display, you must set the column address (0x2A) and page address (0x2B) to the full 480x480 range. Then you switch to RGB mode by sending command 0xB0 with parameter 0x00 (RGB interface mode). After that, the pixel data is sent via the RGB pins, not SPI. The SPI is only used for configuration. If you accidentally send pixel data over SPI, the display will not show anything. Many developers get stuck here because they assume the SPI can also send pixel data. It cannot. The RGB interface is the only path for pixel data once the display is in RGB mode. The TE pin can be used to synchronize frame updates: wait for a rising edge on TE before writing new pixel data to avoid tearing. This is especially important for video playback or animation.

Thermal and Environmental Considerations – The 3.4 inch transmissive TFT LCD operates from -20°C to +70°C. The transmissive technology means the display requires a backlight to be visible; it does not reflect ambient light. In direct sunlight, the brightness of 400 cd/m² (typical) is barely readable. The viewing angle is 80 degrees in all directions (IPS panel). The response time is 25ms (rise + fall). The contrast ratio is 800:1. The pixel pitch is 0.153mm, giving a pixel density of 166 PPI. The display module weight is about 30 grams. The FPC cable is 30mm long from the connector to the glass. Do not bend the FPC more than 10 degrees repeatedly, or the traces will crack. The glass thickness is 0.7mm, and the total module thickness is 2.5mm including the backlight. The active area is 73.44mm x 73.44mm. The outline dimensions are 78.0mm x 78.0mm with a 2.0mm bezel on each side.

Alternative Pinouts – Some 3.4 inch TFT modules from other manufacturers use a different pinout. For example, the Waveshare 3.4 inch round LCD uses a 40-pin FPC with a different arrangement. Always verify the pinout against the specific module datasheet. The DM-TFT34-486 uses the pinout described above, which is compatible with the ST7701S driver IC. If you are using a module with the ILI9488 driver, the pinout is similar but the initialization commands differ. The ILI9488 uses 16-bit RGB (RGB565) instead of 18-bit, so you would only connect the upper 6 bits of each color (R2-R7, G2-G7, B2-B7). The lower bits (R0-R1, G0-G1, B0-B1) would be left unconnected. The SPI commands for the ILI9488 are also different: the command 0x36 for memory access control uses different bit definitions. Check the driver IC datasheet before writing your software.

Testing the Pinout – Before soldering the FPC connector to your final PCB, build a test jig using a 50-pin FPC breakout board. Connect the power pins to a 3.3V supply and the backlight pins to a 3.3V supply through a 10 ohm resistor. Use a logic analyzer to verify the SPI signals: CS should go low before the first clock pulse, and DCX should be stable during the entire byte transfer. For the RGB interface, use an oscilloscope to check the DOTCLK frequency. If the DOTCLK is missing or at the wrong frequency, the display will show a blank screen. The HSYNC and VSYNC signals should be present with the correct polarity (active low). The DE signal should be high only during the active pixel area. If you see DE high during blanking, the image will be shifted. A common test pattern is to send a solid color (e.g., red = 0x3F on the 6-bit red lines) and check if the display shows red. If it shows green or blue, you have swapped the RGB pins. This is the most common wiring error after power issues. If the display shows random noise, the DOTCLK polarity might be inverted. Some driver ICs expect the pixel data to be latched on the rising edge of DOTCLK, others on the falling edge. The ST7701S defaults to rising edge, but you can change it via SPI command 0xB0.