help me

[tieulongnhan9x]

Giúp e cái code mikroC này với. E ko hiểu cái chương trình con getADC().
E ko hiểu ngay chỗ

SPI1_Write(0x06);                     
channel = channel << 6;               
tmp = SPI1_Read(channel) & 0x0F;
tmp = tmp << 8;                      
tmp |= SPI1_Read(0);

tại sao lại viết như vậy?

Bài này là Giao tiếp SPI với con ADC mcp3204.
Nguyên code của nó đây:

sbit Chip_Select_Direction at TRISC0_bit;
sbit Chip_Select at RC0_bit;

// LCD module connections
sbit LCD_RS at RB5_bit;
sbit LCD_EN at RB7_bit;

sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB2_bit;
sbit LCD_D6 at RB4_bit;
sbit LCD_D7 at RB6_bit;

sbit LCD_RS_Direction at TRISB5_bit;
sbit LCD_EN_Direction at TRISB7_bit;

sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB2_bit;
sbit LCD_D6_Direction at TRISB4_bit;
sbit LCD_D7_Direction at TRISB6_bit;
// End LCD module connections

unsigned int  measurement, lastValue;

void Init()
{
  ANSEL  = 0;                                    // Configure AN pins as digital I/O
  ANSELH = 0;
  C1ON_bit = 0;                                  // Disable comparators
  C2ON_bit = 0;

// Init LCD
  Lcd_Init();
  Lcd_Cmd(_LCD_CLEAR);
  Lcd_Cmd(_LCD_CURSOR_OFF);
//

  measurement = 0;                               // Initialize the measurement variable

// Init SPI
  SPI1_Init_Advanced(_SPI_MASTER_OSC_DIV64,      // Initialize PIC as master
                     _SPI_DATA_SAMPLE_END,       // Data sample at end
                     _SPI_CLK_IDLE_LOW,
                     _SPI_LOW_2_HIGH);

  Chip_Select_Direction= 0;                      // ClearBit(TRISC,0)
  Chip_Select= 0;                                // SetBit(PORTC,0)
}

unsigned int getADC(unsigned short channel)
{
 // Returns 0..4095
  unsigned int tmp;
  Chip_Select = 0;                      // Select MCP3204
  SPI1_Write(0x06);                     // SPI communication using 8-bit segments
  channel = channel << 6;               // Bits 7 & 6 define ADC input
  tmp = SPI1_Read(channel) & 0x0F;
  tmp = tmp << 8;                       // Get ADC value
  tmp |= SPI1_Read(0);
  Chip_Select = 1;
  return tmp;
}

void ProcessValue(unsigned int pv, unsigned short channel)
{ // Writes measured values to LCD
  char i, lcdRow, lcdCol;

  if(channel < 2) lcdRow=1;
  else lcdRow=2;
  if(channel%2 > 0 ) lcdCol=13;
  else lcdCol=4;

// Converting the measured value into 4 characters
// and writing them to the LCD at the appropriate place
      i = pv /1000 + 48;
      Lcd_Chr(lcdRow,lcdCol, i);
      pv %= 1000;
      i = pv /100 + 48;
      Lcd_Chr(lcdRow,lcdCol+1, i);
      pv %= 100;
      i = pv /10 + 48;
      Lcd_Chr(lcdRow,lcdCol+2, i);
      pv %= 10;
      i = pv + 48;
      Lcd_Chr(lcdRow,lcdCol+3, i);
}


// main procedure
void main()
{

  Init();
  // Compilation le
  Lcd_Out(1,1,"Build : " __TIME__);
  Lcd_Out(2,1,"le " __DATE__);
  
  Delay_ms(2000);
                                         // Initialize SPI and LCD
  Lcd_Out(1,1,"C0=      C1=");
  Lcd_Out(2,1,"C2=      C3=");

  while(1)
  {
     measurement = getADC(0);                    // Get ADC result from Channel 0
     ProcessValue(measurement,0);                // Writes measured value to LCD
     Delay_ms(100);                              // Wait 100ms
     measurement = getADC(1);                    // Get ADC result from Channel 1
     ProcessValue(measurement,1);                // Writes measured value to LCD
     Delay_ms(100);                              // Wait 100ms
     measurement = getADC(2);                    // Get ADC result from Channel 2
     ProcessValue(measurement,2);                // Writes measured value to LCD
     Delay_ms(100);                              // Wait 100ms
     measurement = getADC(3);                    // Get ADC result from Channel 3
     ProcessValue(measurement,3);                // Writes measured value to LCD
     Delay_ms(100);                              // Wait 100ms
  }
}