MCP3204的C代码如何修改

你好，希望我把这个放在正确的地方！我正在研究一个将MCP74A/D转换器与树莓PI 3模型B接口的项目。实际上，我现在有一些代码运行起来，运行得很好，读取输入0——除了我不完全理解它，以及我将如何修改代码以从其他用途读取。有能力的渠道！让我开始分享我的代码-我不认为这是重要的，如果你不熟悉图书馆在使用中，它是一个相当通用的SPI通信库。我已经通过将PyPIO树莓PI库与许多Python脚本的不同用法一起使用，例如Char WrreEdCMD（3）＝{ 1, 128, 0 }；char Read数据（3）；int速度＝300000；int SPi句柄；int ReADVAL；SpHORADER＝SPIOPEN（0，速度，0）；而（1）{ SPIXFER（SPIHA）NDLE，（CHAR*）和RealEdMCMD，（CHAR*）和Read数据，SIZEOF（Read OpDATA）；ReADVAL＝（（Read OpthDATA（1）和3；lt；lt；8））Read数据（2）；PrimTf（“值：%i n”，ReaDAL）；}如我所说，这个代码似乎工作得很好。我已经做了一些实验，看看速度相对于速度值实际上是在增加和减少，我得到了我所期望的值。下面是我的问题；我在MCP34中写的那些三字节真的是什么？我在数据表（特别是表5-1）上看了很久，我觉得我将发送一个单行字节的二进制数为1×1 dk 0的0（或0x18，假设dk是0），这将表示起始位的1，单端A/D的1，为0的A/D。不必担心，因为我使用MCP324，然后两个零点来请求A/D的信道0，但是，我看到三个字节- 1/128 / 0，这是0 0 0 0 0 0 0 0 1 0，{1×2 }。我一定是误读了数据表！我尝试这样做，发送一个字节24，而不是三，但我真的没有得到任何东西，我希望-胡言乱语，我相信。如果MCP34是一个12位分辨率的A/D转换器，为什么我只得到10位（0？1023）？我可以看到，只有11，最后一个比特是一个符号位或什么，但在这种情况下，我本来希望得到的值范围从0到2047，而不是我现在得到的是0 - 1023。好了，就是这样。希望我已经解释得很好，而且在正确的地方。如果我能做出任何澄清，请告诉我。提前感谢任何建议或指导任何人可能有！恭敬地，Marshall



      以下为原文

    Hello,

Hopefully, I am posting this in the right place!

I am working on a project that interfaces an MCP3204 A/D converter to a Raspberry Pi 3 Model B. I actually now have some code up and running that is working quite well, reading input 0 - except that I don't fully understand it and how I would go about modifying the code to read from the other available channels!
Let me start off by sharing my code - I don't think it matters if you're not familiar with the library in use, it's a fairly generic SPI communications library. I've managed to put this code together by looking at various uses of the pigpio Raspberry Pi library along with a number of python scripts, etc.

char write_cmd[3] = {1, 128, 0};
char read_data[3];
int speed = 300000;
int spiHandle;
int readVal;
spiHandle = spiOpen(0, speed, 0);

while (1)
{
     spiXfer(spiHandle, (char*)&write_cmd, (char*)&read_data, sizeof(read_data));
     readVal = ((read_data[1]&3)<<8) | read_data[2];
     printf("Value: %in",readVal);
}

As I said, this code seems to work quite well. I've done some experimentation to see that the speed is actually increasing and decreasing with respect to the speed value, and I am getting the values that I expect.

Here are my questions;

• What do those three bytes I write into the MCP3204 really do? I've looked long and hard at the data sheet (specifically Table 5-1) and it seems to me that I would be sending in something more along the lines of a single byte with binary 1 1 dk 0 0 (or 0x18, assuming the dk was 0) which would denote a 1 for the start bit, a 1 for single ended A/D, a 0 for the don't care since I'm using the MCP3204, and then two zeros to request channel 0 of the A/D. But instead, I see three bytes - 1/128/0, which is 0 0 0 0 0 0 0 1 | 1 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0. I must be misreading the data sheet! I tried doing this differently, sending in a single byte 24 as opposed to the three, but I don't really get anything back I'd expect - gibberish, I believe.
• If the MCP3204 is a 12 bit resolution A/D converter, why am I only getting 10 bits (0-1023)? I could see maybe only getting 11, with the last bit being a sign bit or something, but in that case, I would have expected to get values ranging from 0 - 2047, instead of what I'm getting now which is 0 - 1023.
  

Ok, that's about it. Hopefully I've explained myself well enough, and in the right place. If there are any clarifications I can make, please let me know. Thanks in advance for any advice or guidance anyone might have!

Respectfully,
Marshall