CC2640 ADC 如何使用外部电压基准？

请教各位大侠！如题，程序中 这样设置后 不起作用：

AUXADCEnableSync(AUXADC_REF_EXT, AUXADC_SAMPLE_TIME_2P73_MS, AUXADC_TRIGGER_MANUAL);

有一些介绍，但是不知该怎么设置。

//! When using external reference voltage, the AUX I/O 7 pin must have been
//! configured in advance. This must be done manually when using DriverLib (the
//! Sensor Controller Interface driver would do this automatically):
//! - Ensure that AUX I/Os are not latched
//! - AUX_AIODIO0: Configure AUX I/O 7 as input/analog with input buffers
//! disabled
//! - IOC: Configure matching DIO pin as AUX I/O with no pull
//!
//! ADC input scaling is enabled by default after calling this function, and
//! must, if desired, be disabled explicitly by calling
//! \ref AUXADCDisableInputScaling().

你好，

CC2640不支持外部参考电压，所以你只能把外部电压分压到内部ADC的参考电压进行模数转换。

希望该回答对你有帮助。

Hi kqian0327,

  感谢您的回答！

  但是我看TI给的2640 DEMO例程中有关于外部基准电压的一些说明，如下，是目前阶段不支持外部参考电压，以后会开放吗？外部基准电压挺常用的功能啊，2541都支持的，我目前遇到的问题是使用VCC做reference 的话，当电池电压下降时会影响测量结果，所以想外加一个精度更高，随电压变化波动比较小的外部参考电源。

//! When using external reference voltage, the AUX I/O 7 pin must have been
//! configured in advance. This must be done manually when using DriverLib (the
//! Sensor Controller Interface driver would do this automatically):
//! - Ensure that AUX I/Os are not latched
//! - AUX_AIODIO0: Configure AUX I/O 7 as input/analog with input buffers
//! disabled
//! - IOC: Configure matching DIO pin as AUX I/O with no pull
//!
//! ADC input scaling is enabled by default after calling this function, and
//! must, if desired, be disabled explicitly by calling
//! \ref AUXADCDisableInputScaling().

没法使用外部，只有内部的两个参考源，参考下面，拿走不谢：

/*!
 *  @brief  Specifies whether the internal reference of the ADC is sourced from the battery voltage or a fixed internal source.
 *
 *  - In practice, using the internal fixed voltage reference sets the upper range of the ADC to a fixed value. That value is 4.3V with
 *  input scaling enabled and ~1.4785V with input scaling disabled. In this mode, the output is a function of the input voltage multiplied
 *  by the resolution in alternatives (not bits) divided by the upper voltage range of the ADC. Output = Input (V) * 2^12 / (ADC range (V))
 *
 *  - Using VDDS as a reference scales the upper range of the ADC with the battery voltage. As the battery depletes and its voltage drops, so does
 *  the range of the ADC. This is helpful when measuring signals that are generated relative to the battery voltage. In this mode, the output is
 *  a function of the input voltage multiplied by the resolution in alternatives (not bits) divided by VDDS multiplied by a scaling factor derived
 *  from the input scaling. Output = Input (V) * 2^12 / (VDDS (V) * Scaling factor), where the scaling factor is ~1.4785/4.3 for input scaling
 *  disabled and 1 for input scaling enabled.
 *
 *  @note   The actual reference values are slightly different for each device and are higher than the values specified above. This gain is saved in
 *          the FCFG. The function ::ADC_convertRawToMicroVolts() must be used to derive actual voltage values. Do not attempt to compare raw values
 *          between devices or derive a voltage from them yourself. The results of doing so will only be approximately correct.
 *
 *  @warning    Even though the upper voltage range of the ADC is 4.3 volts in fixed mode with input scaling enabled, the input should never exceed
 *              VDDS as per the data sheet.
 */
typedef enum ADCCC26XX_Reference_Source {
    ADCCC26XX_FIXED_REFERENCE       = AUXADC_REF_FIXED,
    ADCCC26XX_VDDS_REFERENCE        = AUXADC_REF_VDDS_REL
} ADCCC26XX_Reference_Source;

使用这个参考，两个方式我都试过，都能用，我用的4*4的片子