f31x_adc0_externalinput.c

C8051F31系列单片机的例子

//-----------------------------------------------------------------------------
// F31x_ADC0_ExternalInput.c
//-----------------------------------------------------------------------------
// Copyright 2006 Silicon Laboratories, Inc.
// http://www.silabs.com
//
// Program Description:
// --------------------
//
// This example code takes and averages 2048 analog measurements from input
// P2.5 using ADC0, then prints the results to a terminal window via the UART.
//
// The system is clocked by the internal 24.5MHz oscillator.  Timer 2 triggers
// a conversion on ADC0 on each overflow.  The completion of this conversion
// in turn triggers an interrupt service routine (ISR).  The ISR averages 
// 2048 measurements, then prints the value to the terminal via printf before
// starting another average cycle.
//
// The analog multiplexer selects P2.5 as the positive ADC0 input.  This 
// port is configured as an analog input in the port initialization routine.
// The negative ADC0 input is connected via mux to ground, which provides
// for a single-ended ADC input.
//
// A 100kohm potentiometer may be connected as a voltage divider between 
// P0.0 and AGND on the terminal strip as shown below:
//
// ---------
//          |
//          |
//          |        
//         o| P0.0 ----| 
//         o| GND   ---|<-|
//         o|             |
//         o| P2.5--------|        
//          |
//----------   
// C8051F310-TB
//
// Note that the ADC reference voltage is tied to Vdd, not a precision 
// internal reference.  This limits the precision of the measurement,
// as Vdd is set by the regulator on the board, not the C8051F310.
//
// Terminal output is done via printf, which directs the characters to 
// UART0.  A UART initialization routine is therefore necessary.
//
// ADC Settling Time Requirements, Sampling Rate:
// ----------------------------------------------
//
// The total sample time per input is comprised of an input setting time 
// (Tsettle), followed by a conversion time (Tconvert): 
//
// Tsample  = Tsettle + Tconvert
//
// |--------Settling-------|==Conversion==|----Settling--- . . .
// Timer 2 overflow        ^                          
// ADC0 ISR                               ^       
//
// The ADC input voltage must be allowed adequate time to settle before the 
// conversion is made.  This settling depends on the external source
// impedance, internal mux impedance, and internal capacitance.
// Settling time is given by:
//
//                   | 2^n |
//    Tsettle =   ln | --- | * Rtotal * Csample
//                   | SA  |       
//
// In this application, assume a 100kohm potentiometer as the voltage divider.
// The expression evaluates to:
//
//                   | 2^10 |
//    Tsettle =   ln | ---- | * 105e3 * 5e-12 = 4.4uS
//                   | 0.25 |    
//
// In addition, one must allow at least 1.5uS after changing analog mux 
// inputs or PGA settings.  The settling time in this example, then, is 
// dictated by the large external source resistance.
//
// The conversion is 10 periods of the SAR clock <SAR_CLK>.  At 3 MHz, 
// this time is 10 * 400nS = 3.3 uS.
//
// 
// Tsample, minimum  = Tsettle + Tconvert
//                   = 4.4uS + 3.3uS 
//                   = 7.7 uS
// 
// Timer 2 is set to start a conversion  every 100uS, which is far longer 
// than the minimum required.
//
// F310 Resources:
// ---------------
// Timer1: clocks UART
// Timer2: overflow initiates ADC conversion
//
// How To Test:
// ------------
// 1) Download code to a 'F310 device on a C8051F310-TB development board
// 2) Connect serial cable from the transceiver to a PC
// 3) On the PC, open HyperTerminal (or any other terminal program) and connect
//    to the COM port at <BAUDRATE> and 8-N-1
// 4) Connect a variable voltage source (between 0 and VDD) 
//    to P2.5, or a potentiometer voltage divider as shown above.
// 5) HyperTerminal will print the voltage measured by the device if
//    everything is working properly
//
// FID:            31X000011
// Target:         C8051F310
// Tool chain:     Keil C51 7.50 / Keil EVAL C51
// Command Line:   None
//
//
// Release 1.0
//    -Initial Revision (clm)
//    -24-Jul-06


//-----------------------------------------------------------------------------
// Includes
//-----------------------------------------------------------------------------
#include "c8051F310.h"                 // SFR declarations
#include <stdio.h>

//-----------------------------------------------------------------------------
// 16-bit SFR Definitions for 'F31x
//-----------------------------------------------------------------------------

sfr16 TMR2RL   = 0xca;                 // Timer2 reload value 
sfr16 TMR2     = 0xcc;                 // Timer2 counter
sfr16 ADC0     = 0xbd;                 // ADC0 result

//-----------------------------------------------------------------------------
// Global CONSTANTS
//-----------------------------------------------------------------------------

#define SYSCLK       24500000          // SYSCLK frequency in Hz
#define BAUDRATE     115200            // Baud rate of UART in bps

sbit LED = P3^3;                       // LED='1' means ON

//-----------------------------------------------------------------------------
// Function PROTOTYPES
//-----------------------------------------------------------------------------
void SYSCLK_Init (void);
void PORT_Init (void);
void Timer2_Init(void);
void ADC0_Init(void);
void UART0_Init (void);


void ADC_Init()
{	
    int SARCLK=3000000;	// 3 Mhz
        // Use AD0BUSY as conversion enable
	ADC0CN=0x40;					// ADC with normal track mode
	//REF0CN=0x0e;					// Enable temp sensor and use on chip Vref (VDD)
//	REF0CN=0x0A;					// Enable temp sensor and use on external Vref
	AMX0N=0x1F;						// Single-Ended inputs
	ADC0CF=(SYSCLK/SARCLK-1)<<3;	// Conversion clock setting & results are right-justified
	ADC0CF |= 0x00;                     // right-justify results 
	EIE1 &= 0xF1;					// Disable ADC interrupt & disable win compare interrupts
	AD0EN=1;						// Enable ADC, ready for data conversion
}

unsigned int ADC_Read_Ch(unsigned char chan_num)
{	
    unsigned long result;
	static int measure = 2048;
	static unsigned long accumulator = 0;
	unsigned long mV;                   // measured voltage in mV



	AMX0P = chan_num;					// Select chan to be read thru the MUX
	AD0INT = 0;							// Clear conversion complete indicator
	AD0BUSY = 1;						// Initiate conversion
	
	while (!AD0INT);					// Wait for convesion completed.
	
   

   result = ADC0H;						// Stuff converted data
   result = (result << 8) | ADC0L; 


   accumulator += result;
   measure--;

   if(measure == 0)
   {  
      measure = 2048;
      result = accumulator / 2048;
      accumulator=0;

      // The 10-bit ADC value is averaged across 2048 measurements.  
      // The measured voltage applied to P1.4 is then:
      //
      //                           Vref (mV)
      //   measurement (mV) =   --------------- * result (bits) 
      //                       (2^10)-1 (bits)

      mV =  result * 3250 / 1023;   
      printf("P3.1 voltage: %ld mV\n",mV);
   }

	
	
	return result;
}

//-----------------------------------------------------------------------------
// MAIN Routine
//-----------------------------------------------------------------------------
void main (void) 
{
   PCA0MD &= ~0x40;                    // WDTE = 0 (clear watchdog timer 
                                       // enable)