1.28-inch Round TFT LCD Module, 240x240 px, 4-Wire SPI, GC9A01 Driver, CST816T Capacitive Touch

📥 Download Datasheet (PDF)

This module is a 1.28-inch circular TFT LCD with 240(H)x240(V) pixel resolution, a 4-wire SPI interface driven by the GC9A01 IC, and an integrated CST816T capacitive touch controller. The display area is 32.40x32.40 mm (32.40 mm circular active diameter), the outline is 35.60x37.74x1.62 mm, and the operating temperature range is -20 degrees C to +70 degrees C. All three parameters are confirmed in the product datasheet and define the mechanical, electrical, and environmental integration envelope.

Luminance is rated at 300 cd/m2 from the LED side-light backlight, contrast ratio is 1100:1 in Normally Black mode, and the all-direction viewing angle produces no gray inversion at any off-axis angle. The 262K color depth (18-bit) supports full-color UI rendering including icons, dials, and waveform traces at this pixel density.

Complete specifications

Interface: 4-wire SPI and GC9A01 driver IC

The GC9A01 is a single-chip driver IC designed for circular TFT panels at 240x240 resolution. It accepts pixel data over 4-wire SPI (SCLK, MOSI, CS, DC) and internally manages the column driver, gate driver, and display RAM for the circular panel geometry. No separate frame buffer IC is required; the GC9A01 holds one full 240x240 frame (approximately 112 KB at 16-bit color depth) in its built-in GRAM.

The GC9A01 write SPI clock supports up to 80 MHz per the datasheet. In practice, 40-60 MHz is stable on a custom PCB, and 10-20 MHz on development boards with ribbon-cable connections. At 40 MHz SPI with DMA on an STM32 or ESP32, a full 240x240 RGB565 frame (115,200 bytes) transfers in approximately 23 ms, enabling roughly 40 fps. Open-source drivers exist for Arduino (TFT_eSPI library with GC9A01 driver definition), ESP-IDF, STM32 HAL, MicroPython, and LVGL.

Capacitive touch: CST816T controller, I2C interface, single-point and gesture recognition

The CST816T is a capacitive touch controller integrated on this module alongside the GC9A01 display driver. It communicates with the host over I2C (default address 0x15) and reports single-point X/Y coordinates plus gesture recognition including swipe up, swipe down, swipe left, swipe right, single tap, double tap, and long press. An interrupt output (INT pin) notifies the host on touch events, enabling low-power operation where the MCU enters sleep between touch interrupts.

The CST816T operates on the same 3.3 V supply as the GC9A01 and requires no external calibration for factory-configured circular panels. Pull-up resistors of 4.7 kOhm on SDA and SCL are required if not present on the host development board. The CST816T I2C register map is available in the product datasheet; drivers are included in Arduino libraries compatible with LILYGO T-Display S3 Round and Waveshare RP2040-LCD-1.28, which use the same IC combination.

Round display geometry: 32.40 mm active diameter, 35.60x37.74 mm outline, 1.62 mm depth

The active display area is a 32.40 mm diameter circle within a 32.40x32.40 mm square pixel array. The GC9A01 renders only the circular region; pixels outside the inscribed circle are masked in the driver IC. Host rendering software should apply a circular clip mask at 120 px radius centered at (120, 120) to avoid visual artifacts at the corners of the 240x240 frame buffer. LVGL applies this clip automatically when the circular display flag is set; TFT_eSPI requires manual masking or a filled black circle as the first render layer.

The module outline is 35.60(H)x37.74(V)x1.62 mm maximum depth with a +/-0.1 mm tolerance. The 1.62 mm depth fits standard 2 mm deep LCD pockets in watch-style enclosures without spacer modifications. Pixel pitch is 0.135x0.135 mm (square pixels), giving approximately 188 PPI at the center of the circular active area. At this density, numerals 12 px high are legible at 25 cm viewing distance without custom font hinting.

Optical performance: 300 nit luminance, 1100:1 contrast ratio, all-direction viewing

Luminance is 300 cd/m2 at rated LED backlight current. The 1100:1 contrast ratio in Normally Black mode means off-state pixel luminance is below 0.27 cd/m2, producing a visually dark background for watch-face and dial-style UIs. The all-direction viewing angle (no gray inversion in any direction) maintains image polarity at any viewing angle, which is relevant for wrist-worn devices where display orientation relative to the viewer changes during movement.

The 300 nit luminance is adequate for indoor and sheltered outdoor use. Under direct sunlight (10,000 lux and above), contrast will be reduced; a high-brightness variant at 500-1000 nit is the appropriate specification for sunlight-readable applications. The LED side-light backlight supports PWM dimming; drive the LED enable pin at 1 kHz or higher to avoid visible flicker at reduced brightness levels.

Operating temperature: -20 degrees C to +70 degrees C, storage -30 degrees C to +80 degrees C

The rated operating temperature of -20 degrees C to +70 degrees C covers standard industrial and consumer wearable environments: unheated indoor spaces in winter, vehicle cabin accessories, and portable instruments in temperate climates. Normally Black panel alignment is less sensitive to low-temperature viscosity increases in the liquid crystal layer than Normally White configurations, so cold-start at -20 degrees C does not require a warm-up period before the image stabilizes.

Storage temperature extends to -30 degrees C / +80 degrees C. At the +70 degrees C operating upper limit, LED junction temperature rise will reduce backlight luminance by approximately 10-15% relative to the 25 degrees C rated value. At temperatures above +60 degrees C, reduce LED drive current to the lower end of the rated range to limit thermal accumulation inside compact enclosures.

Target applications for 1.28-inch round TFT LCD modules with capacitive touch

The combination of circular form factor, 4-wire SPI interface, GC9A01 driver, and integrated CST816T capacitive touch makes this module applicable to:

• Smartwatches and fitness trackers where the circular display matches a round watch case and CST816T gesture recognition replaces physical buttons

• MPOS (mobile point-of-sale) terminals displaying transaction status, QR codes, or confirmation prompts on a compact round screen

• Personal navigation devices showing compass bearing or turn indicators in a circular dial format

• Industrial instrument panels with round dial-style readouts for pressure, temperature, or RPM gauges rendered in software

• IoT sensor nodes with ESP32 or RP2040 where the round enclosure aesthetic matches the product design brief and SPI pins are available

Platform compatibility: Arduino, ESP32, STM32, Raspberry Pi, RP2040, and LVGL

The GC9A01 plus CST816T combination is one of the most widely documented 1.28-inch round LCD configurations in the open-source hardware community. Confirmed compatible platforms: ESP32 (Arduino framework via TFT_eSPI with GC9A01 driver definition; ESP-IDF via SPI master driver), RP2040 (MicroPython gc9a01 module; C SDK via direct SPI), STM32F/H series (HAL SPI with GC9A01 init sequence from datasheet), and Raspberry Pi (Python spidev plus smbus2). LVGL supports GC9A01 as a registered display driver, enabling widget-based UI development with circular canvas clipping built into the library.

For the CST816T touch controller, I2C libraries are available for all platforms listed above. The I2C address is fixed at 0x15 on this module configuration. Wire SDA, SCL, INT (interrupt), and RST (reset) from the CST816T pins to the corresponding host GPIO. The LILYGO T-Display S3 Round and Waveshare RP2040-LCD-1.28 BSP source code are direct wiring and firmware references for custom hardware bring-up.

Integration notes and procurement

For initial bring-up, connect the module to an ESP32 or RP2040 development board, flash the TFT_eSPI test sketch (ESP32) or gc9a01 MicroPython example (RP2040), and confirm the GC9A01 responds to the initialization sequence before adding application code. The most common integration failure is incorrect DC (data/command) pin assignment; verify the DC pin in firmware matches the physical pin connected to the module DC line.

When requesting quotation or samples, confirm whether you need the touch version (with CST816T) or the display-only variant, as they share the same PCB outline but differ in connector pin count and I2C wiring. Custom options include circular cover glass with optical bonding, different FPC connector pitch, and conformal coating for humidity resistance. Standard sample lead time is 5-10 business days; custom configuration lead time is 8-12 weeks from specification approval.

FAQ

Q1. Which development boards are confirmed compatible with GC9A01 and CST816T?

A. Confirmed compatible boards include: LILYGO T-Display S3 Round, Waveshare RP2040-LCD-1.28, any ESP32 board with available SPI and I2C pins using TFT_eSPI (GC9A01 driver definition) plus a CST816T I2C library, STM32 Nucleo/Discovery boards with LTDC or SPI peripheral, and Raspberry Pi 3/4/Zero with spidev and smbus2. For Arduino Uno and Nano (AVR), the 5 V logic requires a level shifter on all SPI and I2C lines, and the 2 KB SRAM is insufficient for a full frame buffer; use a 3.3 V ARM-based board instead.

Q2. What SPI clock speed does the GC9A01 support, and what frame rate does that produce?

A. The GC9A01 write SPI clock supports up to 80 MHz per the datasheet. On a well-routed PCB with an STM32 or ESP32, 40-60 MHz is stable, yielding approximately 23-35 ms per full 240x240 RGB565 frame and a practical frame rate of 30-40 fps with DMA. On development boards using ribbon cable or breadboard wiring, 10-20 MHz is more reliable (~92 ms per frame, ~10 fps). Partial-area updates using SET_COLUMN_ADDRESS and SET_ROW_ADDRESS commands reduce transfer time proportionally for regions smaller than the full frame.

Q3. Does the CST816T support multi-touch, and what gestures does it detect?

A. The CST816T supports single-point touch only (one X/Y coordinate at a time). It does not support two-finger pinch or simultaneous multi-point detection. Recognized gestures: swipe up, swipe down, swipe left, swipe right, single tap, double tap, and long press. These are reported via the I2C gesture register alongside the touch coordinate. For multi-touch requirements, a different controller IC (FT5x06 or GT911) with a larger sensor area is needed; contact the applications team with your specification.

Q4. How do I apply a circular clip mask in firmware to avoid corner artifacts?

A. The GC9A01 pixel array is 240x240 square, but the active glass is cut circular. Before writing any pixel to the frame buffer, check whether (x - 120) squared plus (y - 120) squared is less than or equal to 120 squared; skip pixels that fall outside this condition. LVGL handles this automatically when the circular display flag is enabled. TFT_eSPI does not auto-clip; either implement per-pixel masking in the draw callback, or render a filled black circle at radius 120 as the base layer before drawing UI elements. This adds negligible overhead at 40 MHz SPI.

Q5. What is the difference between the touch and display-only variants, and how do I specify the correct one?

A. The display-only variant carries the GC9A01 driver and SPI lines only. The touch variant adds the CST816T capacitive controller, I2C lines (SDA, SCL, INT, RST), and the capacitive sensor film laminated to the front glass. Both share the same 35.60x37.74x1.62 mm outline but differ in FPC pin count. The touch variant is not field-upgradeable from the display-only version. When requesting samples or quotation, state explicitly: part description including CST816T touch, target host processor, interface voltage (1.8 V or 3.3 V logic), and target monthly production volume.