JDI Screen Parameter Configuration

The JDI screen has two types of interfaces: parallel (JDI_PARALLEL) and serial (JDI_SERIAL).

Parallel (JDI_PARALLEL)

Currently, the parallel interface is more common. It generally requires an LCDC and an LP-PWM to work together:

1. LP-PWM (Low power PWM, supports outputting PWM waveforms during system sleep) is used to output the refresh clock XFRP/FRP/VCOM. After 58x, one LP-PWM can control two pin outputs with opposite waveforms.

2. LCDC (LCD Controller) is used to output pixel data and other control signals.

Parameter Configuration Explanation

static LCDC_InitTypeDef lcdc_int_cfg =
{
    .lcd_itf = LCDC_INTF_JDI_PARALLEL,
    .freq = 746268, // HCK frequency

    /* 
        Useless parameter for JDI PARALLEL interface, 
        used to pass the format checking here. 
    */ 
    .color_mode = LCDC_PIXEL_FORMAT_RGB565, 

    .cfg = {
        .jdi = {
            .bank_col_head = 0, // Vertical Blanking pixels at the head
            .valid_columns = THE_LCD_PIXEL_WIDTH, // Vertical valid pixels
            .bank_col_tail = 4, // Vertical Blanking pixels at the tail

            .bank_row_head = 0, // Horizontal Blanking rows at the head
            .valid_rows = THE_LCD_PIXEL_HEIGHT, // Horizontal valid rows
            .bank_row_tail = 4, // Horizontal Blanking rows at the tail

            /* 
                ENB will be active during column [32~95]
            */
            .enb_start_col = 32, 
            .enb_end_col = 95,
        },
    },

};

Refresh Clock

Inside the LCD_DisplayOn and LCD_DisplayOff functions, the output of the PWM device is started and stopped through an externally defined rt_device name (JDI_FRP_LPPWM_INTERFACE_NAME). The purpose is to control the output of FRP/XFRP/VCOM.

The PWM clock frequency is set via the rt_pwm_set interface, as shown in the following code, which sets a 60Hz output with a 50% duty cycle:

/**
  * @brief  Enables the Display.
  * @param  None
  * @retval None
  */
static void LCD_DisplayOn(LCDC_HandleTypeDef *hlcdc)
{
    /* Display On, enable the FRP&XFRP output */
#ifdef JDI_FRP_LPPWM_INTERFACE_NAME
    struct rt_device_pwm *device = (struct rt_device_pwm *)rt_device_find(JDI_FRP_LPPWM_INTERFACE_NAME);
    if (!device)
    {
        LOG_E("Can not find FRP LPPWM device:%s", JDI_FRP_LPPWM_INTERFACE_NAME);
    }
    else
    {
        if (0 == (device->parent.open_flag & RT_DEVICE_OFLAG_OPEN))
        {
            rt_device_open((struct rt_device *)device, RT_DEVICE_OFLAG_RDWR);
            rt_pwm_set(device, 1, 16 * 1000 * 1000, 8 * 1000 * 1000); // Set period to 16ms, pulse to 8ms
            rt_pwm_enable(device, 1); // Enable PWM output
        }
    }
#endif
}

/**
  * @brief  Disables the Display.
  * @param  None
  * @retval None
  */
static void LCD_DisplayOff(LCDC_HandleTypeDef *hlcdc)
{
    /* Display Off, disable the FRP&XFRP output */
#ifdef JDI_FRP_LPPWM_INTERFACE_NAME
    struct rt_device_pwm *device = (struct rt_device_pwm *)rt_device_find(JDI_FRP_LPPWM_INTERFACE_NAME);
    if (!device)
    {
        LOG_E("Can not find FRP LPPWM device:%s", JDI_FRP_LPPWM_INTERFACE_NAME);
    }
    else
    {
        if (device->parent.open_flag & RT_DEVICE_OFLAG_OPEN)
        {
            rt_pwm_disable(device, 1); // Disable PWM output
            rt_device_close((struct rt_device *)device);
        }
    }
#endif
}

Serial (JDI_SERIAL)

We have not tested the serial interface for JDI screens, although it is supported in hardware.