STM32 SPI驱动DAC8830 上电输出不确定电压

只看该作者 · 2015-6-1 17:06

SPI配置函数如下：
void SPI1_DAC8830_Config()
{
GPIO_InitTypeDef GPIO_InitStructure;
SPI_InitTypeDef SPI_InitStructure;

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1,ENABLE);

/* PA5--SCK */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA,&GPIO_InitStructure);

/* PA7--MOSI */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7;
GPIO_Init(GPIOA,&GPIO_InitStructure);

/* PA4--CS for DAC8830 */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_Init(GPIOA,&GPIO_InitStructure);

/* Deselect the DAC8830 */
SPI_DAC8830_CS_High();

/* Configure the SPI Mode */
SPI_InitStructure.SPI_Direction = SPI_Direction_1Line_Tx;
SPI_InitStructure.SPI_CRCPolynomial = 7;
SPI_InitStructure.SPI_DataSize = SPI_DataSize_16b; //Send 16bit
SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB ;
SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_4; // fCLK/4
/* DAC8830 is sampling SDI data at the rising edge */
SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge; //Sampling at odd edge
SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low; //SCK low at the beginnig of CS HIGH to LOW
SPI_Init(SPI1,&SPI_InitStructure);

/* Enable the SPI1 */
SPI_Cmd(SPI1,ENABLE);
}

DAC8830上电会自动复位输出0V。但是执行了上述这个函数之后，每次上电DAC8830就会输出一个不确定的电压，但是SPI配置应该没有问题，因为上电后我在主函数用SPI1和DAC通信时，得到的模拟电压是正确的，只是上电时输出的不为0的电压问题一直困扰我。怀疑是由于PA4（CS信号）上电为低电平，DAC一直处在激活状态，可能从MOSI接口接收了信号造成了输出电压不为0，但是无从验证。求大神帮解答，万分感谢。

1万 · 2015-6-1 17:17

这应该是上电复位的问题, 看 DAC8830 手册的描述:

POWER-ON RESET
Both devices have a power-on reset function to ensure the output is at a known state upon power-up. In the DAC8830 and DAC8831, at power-up, the DAC latch and Input Registers contain all 0s until new data are loaded from the input serial shift register. Therefore, after power-up, the output from pin V OUT of the DAC8830 is 0 V. The output from pin V OUT of the DAC8831 is 0 V in unipolar mode and – V REF in bipolar mode.
However, the serial register of the DAC8830 and DAC8831 is not cleared on power-up, so its contents are undefined. When loading data initially to the device, 16 bits or more should be loaded to prevent erroneous data appearing on the output. If more than 16 bits are loaded, the last 16 are kept; if less than 16 are loaded, bits will remain from the previous word. If the device must be interfaced with data shorter than 16 bits, the data should be padded with 0s at the LSBs.

1万 · 2015-6-1 23:15

这个是，，SPI配置函数。。。电压为啥会不确定呢、、

只看该作者 · 2015-6-2 10:28

zh113214 发表于 2015-6-1 23:15
这个是，，SPI配置函数。。。电压为啥会不确定呢、、

执行了这个函数之后，DAC就输出一个不确定的初始电压，很奇怪

只看该作者 · 2015-6-2 11:38

本帖最后由 GilbertWu 于 2015-6-2 11:41 编辑

airwill 发表于 2015-6-1 17:17
这应该是上电复位的问题, 看 DAC8830 手册的描述:

POWER-ON RESET

  我又认真的看了一遍DAC8830的pdf，时序介绍有一句话：The low-to-high transition of CS transfers the contents of the input shift register to the input register...In the DAC8830, the contents of the input register are transferred into the DAC latch immediately when the input
register is loaded, and the DAC output is updated at the same time.意思是说，CS的低到高变化，会把输入移位寄存器的值送到输入寄存器，而输入寄存器的更新会使DAC立即输出相应的电压。
  而POWER-ON RESET 这里有一句：However, the serial register of the DAC8830 and DAC8831 is not cleared on power-up, so its contents are undefined.姑且认为这里的serial register就是上述的输入移位寄存器。又联想到STM32上电后，PA4端口（CS）默认的是低电平，当我给他Set High时，DAC就会把输入移位寄存器里未知的内容送入输入寄存器，从而DAC输出一个未知的电压值。
  这样理解的话倒是说的通，但是有没有办法避免这个问题？是否有办法让STM上电默认输出高电平呀？

1万 · 2015-6-2 15:37

上电默认输出高电平, 最好加个上拉电阻来实现. 不过我关注的问题是:

However, the serial register of the DAC8830 and DAC8831 is not cleared on power-up, so its contents are undefined. When loading data initially to the device, 16 bits or more should be loaded to prevent erroneous data appearing on the output.

就是说, 上电的寄存器值不确定.

只看该作者 · 2015-11-19 19:17

只看该作者 · 2019-5-20 10:44

您好，我现在也在用DAC8830这款DA，现在遇到了一些问题，请问能否和您交流一下，

只看该作者 · 2023-2-3 15:58

远志昊发表于 2019-5-20 10:44
您好，我现在也在用DAC8830这款DA，现在遇到了一些问题，请问能否和您交流一下， ...

您好，您解决了吗，可以交流交流吗

STM32 SPI驱动DAC8830 上电输出不确定电压

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