PIC初解问题(XC8 MCC)

Question

最近，我让I2C使用一些MCC生成的函数工作，这些函数在.h文件中有很好的文档，但是SPI没有给我任何东西，并且给我带来了麻烦，这并不是因为我对这些串行协议很陌生。

我只是尝试在MCP23S17上读取一个寄存器，然后写入它，然后再读取它以验证它是否改变了。

我甚至不确定我是否会这样做，但我已经将我的代码包含在下面的注释中。出于某些原因，我似乎需要添加一些虚拟写来使第一个读工作，但只发生在第二个循环。

#include "mcc_generated_files/mcc.h"

uint8_t receiveData; /* Data that will be received */
uint8_t OpCodeW = 0x40;
uint8_t OpCodeR = 0x41;

void main(void)
{

    SYSTEM_Initialize();
    INTERRUPT_GlobalInterruptEnable();
    INTERRUPT_PeripheralInterruptEnable();

    Reset1_GPIO_SetLow();
    __delay_ms(200);
    Reset1_GPIO_SetHigh();
    __delay_ms(200);
    
    printf("Initalised \r\n");
    
    while (1)
    {

        SPI1_Open(SPI1_DEFAULT);
        CS1_GPIO_SetLow();
        
        // Read IODIRA Register 0x00
        SPI1_ExchangeByte(OpCodeR);             // Address + Read
        SPI1_ExchangeByte(0x00);                // ??? -- When I add this in it works 2nd loop -- ???
        receiveData = SPI1_ExchangeByte(0x00);  // Returns 0x00 1st loop, then 0xFF after ... 
                                                // ... but only when duplicate sending of byte above ???
        printf("Read IODIRA: 0x%02x \r\n", receiveData);
                                                
         
        // Try writing to IODIRA Register 
        // Not sure what SPI1_WriteByte actually does!
        // I thought it might be the same as ExchangeByte but without anything returned
        // No idea!
        SPI1_WriteByte(OpCodeW);                // Address + Write
        SPI1_WriteByte(0x00);                   // Register Addres IODIRA (Port A)
        SPI1_WriteByte(0xF0);                   // Data to be written
       
        
        // Read back changed IODIRA Register again - Same routine as above
        SPI1_ExchangeByte(OpCodeR);             // Address + Read
        SPI1_ExchangeByte(0x00);                // Same routine as above  ...
                                                // ... but always prints 0x00
        receiveData = SPI1_ExchangeByte(0x00);  // Register Address, IODIRA (Port A)
        printf("Wrote to IODIRA and read back: 0x%02x \r\n", receiveData);    
        
        printf(" ----- \r\n\n");

        CS1_GPIO_SetHigh();               
        SPI1_Close();
        __delay_ms(5000);

    }
}

实际的打印输出如下：

Initalised
Read IODIRA: 0x00    // Should be 0xFF
Wrote to IODIRA and read back: 0x00 // Should be 0xF0
 -----

Read IODIRA: 0xff   // This is right now!
Wrote to IODIRA and read back: 0x00  // but this hasn't changed
 -----

Read IODIRA: 0xff
Wrote to IODIRA and read back: 0x00

Read IODIRA: 0xff
Wrote to IODIRA and read back: 0x00

1. 我的主要问题是，我是否以正确的方式来处理这个问题？
2. 为什么我需要一些虚拟的写来让它在第二个循环上工作？-显然错了。
3. SPI1_ExchangeByte和SPI1_WriteByte有什么区别？
4. 是否有使用这些函数的文档或指南？！？

任何帮助都非常感谢。

Answer 1

答案是需要在每次SPI写入时设置(低)芯片选择，以便在消息启动/完成时通知设备。因为我只想和一个设备交谈，所以我一直在用它来支持(保持设备CS低)，但这是不正确的。