Compose your EIE3810_KeyUp_EXTIInit() for Key_Up.

To initialize the external interrupt for `Key_Up` (connected to EXTI0), you need to follow these steps:

1. **Enable the Clocks**: Enable the clocks for the GPIO and AFIO peripherals.
2. **Configure the GPIO Pin**: Set up the GPIO pin for the key as an input with a pull-up resistor.
3. **Configure the EXTI Line**: Set up the EXTI line to be triggered by the appropriate GPIO pin.
4. **Set the Trigger Type**: Configure the EXTI line to trigger on a falling edge (or rising edge if preferred).
5. **Set the Interrupt Priority**: Assign a priority to the EXTI0 interrupt.
6. **Enable the Interrupt**: Enable the EXTI0 interrupt.

Here is the implementation of `EIE3810_KeyUp_EXTIInit()`:

void EIE3810_KeyUp_EXTIInit(void) {
    // 1. Enable the clocks for GPIOA and AFIO
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);

    // 2. Configure GPIOA Pin 0 (Key_Up) as input with pull-up resistor
    GPIO_InitTypeDef GPIO_InitStructure;
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU; // Input Pull-Up
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    // 3. Configure EXTI Line 0 to be mapped to PA0
    GPIO_EXTILineConfig(GPIO_PortSourceGPIOA, GPIO_PinSource0);

    // 4. Set the trigger type for EXTI Line 0 (falling edge)
    EXTI_InitTypeDef EXTI_InitStructure;
    EXTI_InitStructure.EXTI_Line = EXTI_Line0;
    EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
    EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;
    EXTI_InitStructure.EXTI_LineCmd = ENABLE;
    EXTI_Init(&EXTI_InitStructure);

    // 5. Set the priority for EXTI Line 0
    NVIC_InitTypeDef NVIC_InitStructure;
    NVIC_InitStructure.NVIC_IRQChannel = EXTI0_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x75 >> 4; // Higher 4 bits of 0x75
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x75 & 0x0F; // Lower 4 bits of 0x75
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);
}

### Explanation:
1. **Enable the Clocks**:
- `RCC_APB2PeriphClockCmd` enables the clocks for GPIOA and AFIO.

2. **Configure the GPIO Pin**:
- `GPIO_InitTypeDef` initializes the GPIO structure.
- `GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;` sets the pin to PA0.
- `GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;` configures the pin as an input with a pull-up resistor.
- `GPIO_Init(GPIOA, &GPIO_InitStructure);` applies the configuration to GPIOA.

3. **Configure the EXTI Line**:
- `GPIO_EXTILineConfig` maps EXTI Line 0 to PA0.

4. **Set the Trigger Type**:
- `EXTI_InitTypeDef` initializes the EXTI structure.
- `EXTI_InitStructure.EXTI_Line = EXTI_Line0;` specifies EXTI Line 0.
- `EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;` sets the mode to interrupt.
- `EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;` sets the trigger type to falling edge.
- `EXTI_InitStructure.EXTI_LineCmd = ENABLE;` enables the EXTI line.
- `EXTI_Init(&EXTI_InitStructure);` applies the configuration.

5. **Set the Priority**:
- `NVIC_InitTypeDef` initializes the NVIC structure.
- `NVIC_InitStructure.NVIC_IRQChannel = EXTI0_IRQn;` specifies the EXTI0 interrupt channel.
- `NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x75 >> 4;` sets the pre-emption priority (higher 4 bits of 0x75).
- `NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x75 & 0x0F;` sets the sub-priority (lower 4 bits of 0x75).
- `NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;` enables the interrupt channel.
- `NVIC_Init(&NVIC_InitStructure);` applies the configuration.

This function sets up the external interrupt for `Key_Up` (EXTI0) to be triggered on a falling edge and assigns it a specific priority.