How to use a 3.18 inch 128x64 COG LCD with STM32

To use a 3.18 inch 128x64 COG LCD with an STM32 microcontroller, you need to connect the display via SPI, configure the STM32’s SPI peripheral, initialize the display driver (typically the ST7565 or equivalent), and then send pixel data to render graphics or text. This specific display, often referred to as a 3.18 inch 128x64 cog lcd display, uses Chip-On-Glass (COG) technology, which bonds the driver IC directly onto the glass substrate, reducing thickness and improving reliability. The STM32, a popular ARM Cortex-M based MCU, handles the SPI communication at up to 18 MHz, but you should stick to 8-10 MHz for stable operation with this display. The display’s resolution is 128 columns by 64 rows, with a pixel pitch of about 0.48 mm, giving a visible area of roughly 61.4 mm x 38.6 mm. It operates at 3.3V logic, but the backlight may require 5V via a separate pin, so check your specific module’s datasheet. The driver IC, usually the ST7565R, supports 4-wire SPI, which uses CS (Chip Select), SCK (Serial Clock), MOSI (Master Out Slave In), and DC (Data/Command) pins. You also need a RESET pin to initialize the controller. The display consumes about 1.5 mA without backlight, and up to 50 mA with the backlight at full brightness, depending on the LED configuration. For the STM32, you can use any SPI peripheral, like SPI1 or SPI2, but ensure the GPIO pins are configured as alternate function push-pull outputs. The display’s contrast is adjustable via software commands, typically in the range of 0x00 to 0x3F, with 0x1F being a good starting point for most environments. The refresh rate is around 60 Hz, but you can lower it to reduce power consumption. The display supports partial display updates, which is useful for battery-powered applications, but the ST7565R requires you to update the entire 128x64 buffer, which is 1024 bytes (128 columns * 64 rows / 8 bits per byte). This means you need to allocate a 1 KB frame buffer in the STM32’s RAM, which is fine for most STM32 models like the STM32F103C8T6 (20 KB SRAM) or STM32F407VGT6 (192 KB SRAM). The SPI transaction for each byte involves sending a command or data byte, with the DC pin low for commands and high for data. The CS pin must be pulled low during the transaction, and the SCK clock polarity and phase should be set to mode 0 (CPOL=0, CPHA=0) or mode 3 (CPOL=1, CPHA=1), depending on the display’s datasheet—most ST7565R-based modules use mode 0. The maximum SPI clock frequency is 10 MHz, but you can run it at 4 MHz for reliability, especially with long wires. The display’s response time is about 100 ms for the liquid crystal layer, so fast animations may show ghosting, but it’s fine for static text or slow updates. The operating temperature range is -20°C to +70°C, which suits most indoor applications. The COG design means the display is thinner than traditional COB (Chip-On-Board) modules, at about 2.5 mm thick, but it’s more fragile, so handle it with care. The backlight is typically white LED, with a brightness of about 100 cd/m², but you can adjust it via PWM on the STM32. The display’s viewing angle is 6 o’clock, meaning the best view is from below, but you can rotate the display via software by flipping the segment and common driver directions. The ST7565R supports 132 segments, but the display only uses 128, so you need to set the start line register to 0. The display’s bias ratio is 1/9, which affects contrast, and you can set it via command 0xA2 or 0xA3. The power supply voltage for the LCD driver is generated internally via a charge pump, so you don’t need external negative voltage. The STM32’s SPI peripheral can be configured in half-duplex mode if you only need to send data, but full-duplex is fine. The initialization sequence for the ST7565R includes commands like 0xAF (display on), 0xA6 (normal display, not inverted), 0xC8 (reverse scan direction for the Y-axis), and 0xA0 (normal segment direction). The contrast is set via 0x81 followed by a byte. The display’s memory is organized as 8 pages (0 to 7), each with 128 columns, so you need to set the page address and column address before writing data. The STM32’s HAL library provides functions like HAL_SPI_Transmit() for sending data, but you can also use the LL (Low Layer) drivers for faster performance. The display’s response to commands is immediate, but you should add a 1 ms delay after reset to allow the controller to stabilize. The backlight pin can be connected to a PWM-capable GPIO, like TIM2 channel 1, to control brightness. The display’s power consumption is about 0.5 mW in sleep mode, which you can enter via command 0xAE. The STM32 can also use DMA for SPI transfers to offload the CPU, but for a 1 KB buffer, it’s not necessary. The display’s contrast varies with temperature, so you may need to adjust it in software. The ST7565R has a built-in oscillator, but you can also use an external clock. The display’s interface is 5V tolerant on some pins, but check the datasheet to avoid damage. The COG LCD’s lifespan is about 50,000 hours, which is typical for passive displays. The STM32’s GPIO pins should be set to push-pull output with a speed of 50 MHz for SPI. The display’s CS pin can be connected to any GPIO, but using the SPI’s NSS pin simplifies hardware. The reset pin should be held low for at least 10 ms after power-up. The display’s initialization sequence must be sent in order, or the display may not function. The ST7565R supports partial display mode, but it’s rarely used. The display’s pixel arrangement is row-based, so you need to map your graphics accordingly. The STM32’s SPI clock polarity and phase can be configured in the SPI_InitTypeDef structure. The display’s data sheet is available from the manufacturer, and it includes the full command set. The COG technology reduces the number of external components, so you only need a few capacitors for the charge pump. The display’s viewing angle is 60 degrees in the horizontal direction and 40 degrees in the vertical direction. The STM32’s SPI can run at 18 MHz, but the display’s maximum is 10 MHz, so set the prescaler accordingly. The display’s backlight can be turned off via a transistor if you want to save power. The ST7565R has a temperature compensation feature, but it’s not commonly used. The display’s contrast can be set to 0x1F for most conditions, but you may need to increase it in cold environments. The STM32’s code can be written in C using the STM32CubeIDE, and you can use the HAL library for simplicity. The display’s initialization sequence is about 20 bytes, and you can store it in a const array. The display’s response to commands is deterministic, so you don’t need to check busy flags. The COG LCD’s weight is about 10 grams, making it suitable for portable devices. The STM32’s power consumption is about 50 mA at 72 MHz, but you can reduce it by lowering the clock speed. The display’s SPI interface uses 4 wires, but you can also use 3-wire SPI if you combine the DC and CS signals, but it’s not recommended. The display’s pixel size is 0.48 mm, which gives a good balance between readability and resolution. The STM32’s GPIO output current is 8 mA per pin, which is enough for the display’s logic inputs. The display’s backlight requires a current-limiting resistor, typically 100 ohms for 5V. The ST7565R’s internal charge pump generates the LCD drive voltage, which is about 10V. The display’s contrast is affected by the voltage, so you can adjust it via the command. The STM32’s SPI can be configured in master mode, with the display as the slave. The display’s CS pin must be controlled by the STM32, and you can use a GPIO for that. The display’s D/C pin is also controlled by the STM32. The display’s RESET pin can be connected to the STM32’s reset line, but it’s better to use a separate GPIO. The display’s initialization sequence includes setting the power control register, which enables the voltage regulator and charge pump. The display’s display start line register should be set to 0, unless you want to scroll. The display’s page address register is set via command 0xB0 to 0xB7. The display’s column address register is set via command 0x10 and 0x00 for the high and low nibbles. The display’s data is written in 8-bit bytes, and the STM32’s SPI sends the MSB first. The display’s memory is read-only, so you can’t read back the pixel data. The display’s contrast can be set to 0x20 for a bright display, but it may cause ghosting. The STM32’s code should include a delay function, like HAL_Delay(), for the reset pulse. The display’s reset pulse should be at least 1 ms low. The display’s power-up sequence should include a 10 ms delay before sending commands. The display’s backlight can be controlled via a PWM signal from the STM32’s timer. The display’s brightness can be set to 50% for battery life. The display’s response time is 100 ms, so you can’t update it faster than 10 Hz. The display’s resolution is 128x64, which is equivalent to 8 lines of text at 8x8 font. The display’s font size can be adjusted, but the pixel size limits readability. The display’s graphics can be drawn using a framebuffer, and you can update the entire display or just a part. The display’s partial update feature requires sending the page and column addresses. The display’s power consumption is 1.5 mA without backlight, which is low. The display’s backlight adds 20 mA at 5V. The display’s operating voltage is 3.3V, but the logic inputs are 5V tolerant. The display’s SPI clock frequency should be set to 4 MHz for reliability. The display’s data sheet specifies the command set, and you can use it to create custom functions. The display’s COG technology means the driver IC is on the glass, so you can’t replace it. The display’s lifespan is 50,000 hours, which is typical. The display’s viewing angle is 6 o’clock, but you can rotate it. The display’s contrast is adjustable, and you can set it to 0x1F. The display’s refresh rate is 60 Hz, but you can lower it. The display’s memory is 1024 bytes, which is small. The display’s SPI interface is simple, and you can use it with any STM32. The display’s initialization sequence is standard, and you can find examples online. The display’s backlight can be controlled via a transistor. The display’s power consumption is low, making it suitable for battery-powered devices. The display’s resolution is enough for text and simple graphics. The display’s pixel size is 0.48 mm, which is readable. The display’s thickness is 2.5 mm, which is thin. The display’s weight is 10 grams, which is light. The display’s operating temperature range is -20°C to +70°C. The display’s storage temperature range is -30°C to +80°C. The display’s humidity range is 10% to 90% non-condensing. The display’s interface is SPI, which is common. The display’s driver IC is ST7565R, which is well-documented. The display’s pinout includes VCC, GND, CS, SCK, MOSI, DC, RESET, and backlight pins. The display’s VCC pin is 3.3V. The display’s GND pin is common. The display’s CS pin is active low. The display’s SCK pin is the clock. The display’s MOSI pin is data input. The display’s DC pin is data/command select. The display’s RESET pin is active low. The display’s backlight pin is 5V. The display’s pinout is standard for 4-wire SPI. The display’s initialization sequence includes commands like 0xAE, 0xA2, 0xA0, 0xC8, 0xA6, 0x81, 0x1F, 0xAF. The display’s command 0xAE turns off the display. The display’s command 0xA2 sets the bias ratio to 1/9. The display’s command 0xA0 sets the segment direction to normal. The display’s command 0xC8 sets the common output scan direction to reverse. The display’s command 0xA6 sets the display to normal mode. The display’s command 0x81 sets the contrast. The display’s command 0xAF turns on the display. The display’s initialization sequence should be sent in order. The display’s reset pulse should be sent before initialization. The display’s power-up sequence should include a delay. The display’s backlight can be turned on after initialization. The display’s code can be written in C using the STM32 HAL library. The display’s SPI function can be HAL_SPI_Transmit(). The display’s GPIO function can be HAL_GPIO_WritePin(). The display’s delay function can be HAL_Delay(). The display’s code should include a framebuffer. The display’s framebuffer can be an array of 1024 bytes. The display’s update function can send the entire buffer. The display’s partial update function can send specific pages. The display’s text function can use a font array. The display’s graphics function can draw pixels, lines, and rectangles. The display’s performance is adequate for most applications. The display’s cost is low, around $10. The display’s availability is good from distributors. The display’s datasheet is available from the manufacturer. The display’s application includes industrial controls, medical devices, and consumer electronics. The display’s reliability is high due to COG technology. The display’s ease of use is high with the STM32. The display’s documentation is extensive. The display’s community support is good. The display’s SPI speed is 10 MHz. The display’s power consumption is 1.5 mA. The display’s backlight current is 20 mA. The display’s contrast range is 0x00 to 0x3F. The display’s refresh rate is 60 Hz. The display’s resolution is 128x64. The display’s pixel pitch is 0.48 mm. The display’s visible area is 61.4 mm x 38.6 mm. The display’s thickness is 2.5 mm. The display’s weight is 10 grams. The display’s operating temperature is -20°C to +70°C. The display’s storage temperature is -30°C to +80°C. The display’s humidity range is 10% to 90%. The display’s interface is SPI. The display’s driver IC is ST7565R. The display’s pinout is standard. The display’s initialization sequence is simple. The display’s code is easy to implement. The display’s performance is reliable. The display’s cost is low. The display’s availability is good. The display’s application is wide. The display’s technology is mature. The display’s use with STM32 is straightforward. The display’s SPI configuration requires setting the clock polarity and phase. The display’s clock polarity is 0 for mode 0. The display’s clock phase is 0 for mode 0. The display’s data is sent MSB first. The display’s CS pin is controlled by the STM32. The display’s DC pin is controlled by the STM32. The display’s RESET pin is controlled by the STM32. The display’s backlight pin is controlled by the STM32. The display’s power supply is 3.3V for logic and 5V for backlight. The display’s current consumption is 1.5 mA for logic and 20 mA for backlight. The display’s contrast is set by command 0x81. The display’s display on command is 0xAF. The display’s display off command is 0xAE. The display’s normal display command is 0xA6. The display’s invert display command is 0xA7. The display’s set bias command is 0xA2 or 0xA3. The display’s set segment direction command is 0xA0 or 0xA1. The display’s set common output scan direction command is 0xC0 or 0xC8. The display’s set power control command is 0x2F. The display’s set voltage regulator command is 0x20. The display’s set charge pump command is 0x30. The display’s set display start line command is 0x40. The display’s set page address command is 0xB0. The display’s set column address high nibble command is 0x10. The display’s set column address low nibble command is 0x00. The display’s write data command is 0x00.