F28335 SPI低电平为什么是2V？

只看该作者 · 2014-10-3 21:34

如题，我用示波器测量SPI的波形，高电平是3.3v没问题，为什么低电平是2v？下面是我的程序

#include "DSP2833x_Device.h"    // DSP2833x Headerfile Include File
#include "DSP2833x_Examples.h" // DSP2833x Examples Include File

//#define    LedReg (*((volatile  Uint16 *)0x41FF))
//Uint16 *ExRamStart = (Uint16 *)0x100000;

void spi_xmit(Uint16 a);
void spi_fifo_init(void);
void spi_init(void);

void main(void)
{
Uint16 sdata;  // send data
Uint16 rdata;  // received data

InitSysCtrl();

InitXintf16Gpio(); //zq

InitSpiaGpio();

DINT;

InitPieCtrl();

// Disable CPU interrupts and clear all CPU interrupt flags:
IER = 0x0000;
IFR = 0x0000;

InitPieVectTable();

spi_fifo_init();    // Initialize the Spi FIFO
spi_init();    // init SPI

sdata = 0xAAAA;
for(;;)
{
   // Transmit data
spi_xmit(sdata);
   // Wait until data is received
   while(SpiaRegs.SPIFFRX.bit.RXFFST !=1) { }
   // Check against sent data
   rdata = SpiaRegs.SPIRXBUF;

   //sdata++;

}
}
void spi_init()
{
SpiaRegs.SPICCR.all =0x000F;                // Reset on, rising edge, 16-bit char bits
SpiaRegs.SPICTL.all =0x0086;       // Enable master mode, with phase delay,
                                             // enable talk, and SPI int disabled.
SpiaRegs.SPIBRR =0x006; //波特率7.5MHz
SpiaRegs.SPICCR.all =0x008F;          // Relinquish SPI from Reset
SpiaRegs.SPIPRI.bit.FREE = 1;             // Set so breakpoints don't disturb xmission
}

void spi_xmit(Uint16 a)
{
SpiaRegs.SPITXBUF=a;
}

void spi_fifo_init()
{
// Initialize SPI FIFO registers
SpiaRegs.SPIFFTX.all=0xE040;
SpiaRegs.SPIFFRX.all=0x205f;
SpiaRegs.SPIFFCT.all=0x0;
}
（顺便说一下，f28335的芯片资料上SPI波形的高电平不知道为什么是5v，是不是错了）