What is the interface type for a 1.14 inch 240x135 LCD?

The interface type for a 1.14 inch 240x135 LCD is almost exclusively SPI (Serial Peripheral Interface), specifically 4-wire SPI, with a few variants like 3-wire SPI or 9-bit SPI depending on the driver IC. You won’t find parallel interfaces like 8080 or 6800 on these tiny displays because the pin count would be too high for such a small form factor. The most common driver ICs are the ST7789V or GC9A01, both of which natively support SPI. For example, the widely used 1.14 inch 240x135 ips display from DisplayModule uses the ST7789V driver and operates via 4-wire SPI, which includes MOSI (Master Out Slave In), MISO (Master In Slave Out—though often unused or tied to ground), SCLK (Serial Clock), and CS (Chip Select), plus DC (Data/Command) and RST (Reset) lines. The SPI clock speed can go up to 62.5 MHz with the right microcontroller, but typical implementations run at 20–40 MHz for stable operation.

Let’s break down the technical specifics. The 1.14 inch 240x135 LCD uses a 262K color depth (RGB 6-6-6) with a pixel format of 240 columns by 135 rows, which is a non-standard resolution often called “roundish” or “square-ish” because it’s designed for smartwatches or small IoT devices. The SPI interface is mandatory because the display controller is integrated into the glass itself—the driver IC is bonded directly to the LCD panel via COG (Chip-on-Glass) technology. The ST7789V, for instance, supports SPI mode 0 (CPOL=0, CPHA=0) and mode 3 (CPOL=1, CPHA=1), but most libraries default to mode 0. The data transfer rate is critical: at 240x135 pixels, each frame requires 240 * 135 * 18 bits (for 262K color) = 583,200 bits, or about 72.9 KB per frame. At 30 FPS, that’s 2.18 MB/s, which is easily handled by SPI at 20 MHz (2.5 MB/s theoretical). But if you’re pushing 60 FPS, you’d need 4.36 MB/s, so a 40 MHz SPI clock is safer. Some cheaper clones use the GC9A01 driver, which is almost identical but has slightly different command sets for sleep modes and gamma correction.

Now, let’s talk about the physical pinout. A typical 1.14 inch 240x135 LCD module has 6 or 7 pins for SPI control. Here’s a common pinout table for a 6-pin variant (without MISO):

Pin Name	Function	Notes
VCC	Power Supply	2.8V to 3.3V typical, 5V tolerant with regulator
GND	Ground	Common ground
SCL	SPI Clock	Up to 62.5 MHz, but 20-40 MHz recommended
SDA	SPI Data (MOSI)	Data input, half-duplex
RES	Reset	Active low, tied to VCC if not used
DC	Data/Command	High for data, low for command
CS	Chip Select	Active low, can be tied to GND for single device

Some modules add a BL (Backlight) pin, which is usually a PWM input for brightness control. The backlight LED forward voltage is around 3.0V to 3.3V at 20 mA, so you can drive it directly from a GPIO or through a transistor. The SPI interface here is not just for pixel data—it also sends initialization commands like SLPOUT (0x11) to exit sleep mode, MADCTL (0x36) for orientation, and COLMOD (0x3A) to set pixel format to 18-bit. The ST7789V datasheet specifies a minimum SPI clock high/low time of 8 ns, which translates to a theoretical max of 62.5 MHz, but real-world PCB traces and parasitic capacitance limit it to about 40 MHz on breadboards.

Now, let’s get into the electrical characteristics because this matters for real-world design. The ST7789V operates at 1.65V to 3.3V for logic, but the LCD panel itself requires a boost converter to generate the gate driver voltages (around 15V to 20V). The typical power consumption is 3.5 mA at 3.3V with all pixels white, and 5.5 mA with a full black pattern (because the IPS panel uses a normally black mode, so more voltage is needed to turn pixels on). The SPI interface draws negligible current—the main draw is the backlight (20 mA) and the gate driver. For battery-powered devices, you can use the SLPIN (0x10) command to put the display into sleep mode, dropping consumption to 0.5 µA. The SPI lines must be pulled up to VCC with 10k resistors if you’re using open-drain outputs, but most microcontrollers use push-pull, so you can skip that.

There’s also a 3-wire SPI variant used in some modules, where the DC line is eliminated and the data/command bit is encoded in the first byte of each SPI transaction. This is often called “9-bit SPI” because you send 9 bits per word: the first bit indicates command (0) or data (1), and the next 8 bits are the actual byte. This reduces pin count to 5 (VCC, GND, SCL, SDA, CS) but requires software manipulation in the microcontroller. The GC9A01 driver supports this mode natively, but the ST7789V does not—it requires a separate DC pin. So if you see a 5-pin module, it’s likely using a GC9A01 or a custom firmware. The 1.14 inch 240x135 ips display from DisplayModule uses the 4-wire SPI with DC, which is more compatible with standard libraries like Adafruit_GFX or TFT_eSPI.

Now, let’s talk about timing diagrams because that’s where the rubber meets the road. In SPI mode 0, data is sampled on the rising edge of SCLK and shifted on the falling edge. The ST7789V requires a minimum SCLK period of 16 ns (62.5 MHz), but the setup time for data before the rising edge is 5 ns, and hold time is 2 ns. The CS line must be low for at least 5 ns before the first SCLK edge, and high for 5 ns after the last. The DC line must be stable for 5 ns before the rising edge of SCLK for the first bit. These are tight but easily met by any modern microcontroller like ESP32 (which can do 80 MHz SPI) or RP2040 (up to 50 MHz). However, if you’re using an Arduino Uno (16 MHz), the SPI clock is limited to 8 MHz (half of system clock), so you’ll get about 1 MB/s throughput, which is fine for static images but not for video.

Here’s a real-world performance comparison for different microcontrollers driving the 1.14 inch 240x135 LCD via SPI:

Microcontroller	SPI Clock (MHz)	Max Frame Rate (FPS)	Notes
ESP32	40	60	DMA capable, 240 MHz CPU
RP2040 (Pico)	50	75	PIO state machine, no DMA overhead
Arduino Uno	8	12	No DMA, 16 MHz CPU
STM32F103	36	54	DMA with SPI, 72 MHz CPU

The frame rates assume full 18-bit color and no overclocking. With 16-bit color (RGB 5-6-5), you can squeeze about 20% more FPS because you’re sending 16 bits per pixel instead of 18. The ST7789V supports both 16-bit and 18-bit modes via the COLMOD register. Most libraries default to 16-bit for speed, but the display’s native color depth is 18-bit, so you lose some color fidelity. The SPI interface is the bottleneck here—not the display’s response time. The ST7789V has a typical response time of 10 ms, which is 100 FPS capable, but SPI can’t keep up at that speed unless you use a parallel interface (which doesn’t exist on this form factor).

Now, let’s address the MISO pin situation. On most 1.14 inch 240x135 LCD modules, the MISO pin is either not connected or tied to ground. The ST7789V does have a MISO output, but it’s only used for reading the display’s internal registers (like the pixel format or status). You rarely need to read back from the display—it’s a write-only device for most applications. So, many modules omit the MISO pin to save space. The 4-wire SPI is actually a 3-wire plus DC, but it’s still called 4-wire because the industry standard counts CS as a wire. Some datasheets refer to it as “3-line SPI” if they exclude CS and tie it to ground, but that’s risky because you can’t share the bus with other SPI devices.

There’s also a QSPI (Quad SPI) variant on some larger displays, but not on the 1.14 inch ones. The ST7789V does support QSPI in theory, but the pinout for QSPI requires four data lines (IO0, IO1, IO2, IO3), which would require a 10-pin connector or more. Given the tiny PCB size (usually 18mm x 28mm), manufacturers stick to the standard 6-pin or 7-pin SPI. The 1.14 inch 240x135 ips display from DisplayModule uses a 6-pin 0.5mm pitch FPC connector, which is common for wearable devices. The FPC cable is typically 15mm long and can be bent at 90 degrees, but the SPI signal integrity degrades if you bend it too sharply—keep the bend radius above 3mm.

Let’s talk about software compatibility. The SPI interface for this display is identical to the popular 1.3 inch 240x240 round LCD, so you can use the same libraries with minor tweaks to the resolution. The TFT_eSPI library for ESP32 has a dedicated configuration file (User_Setup.h) where you set the SPI pins, the driver IC (ST7789), and the resolution (240x135). The initialization sequence is standard: send a software reset (0x01), wait 120 ms, send sleep out (0x11), wait 120 ms, set color mode (0x3A with 0x05 for 16-bit or 0x06 for 18-bit), set memory access control (0x36 with 0x00 for portrait), set column address (0x2A) and page address (0x2B) to 0-239 and 0-134, then send RAM write (0x2C). The SPI transaction must be wrapped with CS low and high, and the DC line toggled appropriately. If you’re using an Arduino, the Adafruit_ST7789 library works out of the box, but you need to define the SPI pins manually because the library assumes a specific pinout for the breakout board.

Now, let’s get into the electrical noise considerations. The SPI bus on these displays is sensitive to crosstalk from adjacent wires, especially if you’re using long jumper wires on a breadboard. The SCLK line can radiate noise if you run it at 40 MHz, and the SDA line can pick up that noise. Keep the SPI traces short (under 10 cm) and avoid running them parallel to power lines. Use a 100nF decoupling capacitor on the VCC pin as close to the display as possible. The reset pin should have a 10k pull-up resistor to VCC to prevent accidental resets from noise. Some modules include a built-in capacitor, but it’s better to add your own. The backlight pin can be driven by a PWM signal from the microcontroller, but if you’re using a high-frequency PWM (like 1 kHz or more), the switching noise can couple into the SPI lines. Use a low-pass filter (10 ohm resistor + 100nF capacitor) on the backlight pin to reduce this.

Let’s also talk about power sequencing. The ST7789V requires a specific power-up sequence: VCC must be stable for at least 10 ms before