f31x_adc0_externalinput_mux.c

C8051F31系列单片机的例子

//-----------------------------------------------------------------------------
// F31x_ADC0_ExternalInput_Mux.c
//-----------------------------------------------------------------------------
// Copyright 2005 Silicon Laboratories, Inc.
// http://www.silabs.com
//
// This code example illustrates using the internal analog multiplexer to
// measure analog voltages on up to 8 different analog inputs.  Results are
// printed to a PC terminal program via the UART.
//
// The inputs are sequentially scanned, beginning with input 0 (P1.0), up
// to input number <ANALOG_INPUTS>-1 based on the values in <PIN_TABLE>.
//
//
// 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 and conversion times may overlap, as the ADC holds the value once
// conversion begins.  This program takes advantage of this to increase the
// settling time above the minimum required.  In other words, when
// converting the value from analog input Ain(n), the input mux is switched
// over to the next input Ain(n+1) to begin settling.
//
// |---Settling Ain(n)---|=Conversion Ain(n)=|
//                       |---Settling Ain(n+1)---|=Conversion Ain(n+1)=|
//                                               |---Settling Ain(n+2)---|
// ISR:  Timer 2         ^                       ^                       ^
// ISR:  ADC0                                ^                         ^
//
// 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:
//
//                   | 2^12 |
//    Tsettle =   ln | ---- | * 105e3 * 10e-12 = 10.2uS
//                   | 0.25 |
//
// In addition, one must allow at least 1.5 us 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 16 periods of the SAR clock.  At 2.5 MHz,
// this time is 16 * 400nS = 6.4 uS.
//
//
// Tsample, minimum  = Tsettle + Tconvert
//                   = 10.2uS + 6.4uS
//                   = 16.6 uS
//
// Timer2 is set to change the MUX input and start a conversion every 20 us.
//
// General:
// --------
//
// The system is clocked using the internal 24.5MHz oscillator. Results are
// printed to the UART from a loop with the rate set by a delay based on
// Timer0. This loop periodically reads the ADC value from a global array,
// <RESULT>.
//
// The ADC makes repeated measurements at 20 us intervals based on Timer2.
// The end of each ADC conversion initiates an interrupt which calls an
// averaging function. <INT_DEC> samples are averaged, then the Result
// values updated.
//
// For each power of 4 of <INT_DEC>, you gain 1 bit of effective resolution.
// For example, <INT_DEC> = 256 gain you 4 bits of resolution: 4^4 = 256.
//
// The ADC input multiplexer is set for a single-ended input.  The example
// sequentially scans through the inputs, starting at P1.0.  <ANALOG_INPUTS>
// inputs are read.  The amplifier is set for unity gain so a voltage range of
// 0 to Vref (2.43V) may be measured.  Although voltages up to Vdd may be
// applied without damaging the device, only the range 0 to Vref may be
// measured by the ADC.
//
// A 100 kohm potentiometer may be connected as a voltage divider between
// VREF and AGND as shown below:
//
// ---------
//          |
//         o| AGND ----|
//         o| VREF ----|<-|
//         o| P1.x     |  |
//         o|    |        |
//         o|     --------
//         o|
//         o|
//         o|
//          |
// ---------
//
// How To Test:
//
// 1) Download code to a 'F31x device that is connected to a UART transceiver
// 2) Verify the TX and RX jumpers are populated on J3.
// 3) Connect a serial cable from the DB9 connector to a PC
// 4) On the PC, open HyperTerminal (or any other terminal program) and connect
//    to the COM port at <BAUDRATE> and 8-N-1
// 5) Connect a variable voltage source (between 0 and Vref) to the Port1 pins,
//    or a potentiometer voltage divider as shown above.
// 6) HyperTerminal will print the voltages measured by the device if
//    everything is working properly.  Note that some of the analog inputs are
//    floating and will return nonzero values.
//
// Target:         C8051F31x
// Tool chain:     Keil C51 7.50 / Keil EVAL C51
// Command Line:   None
//
// Release 1.0
//    -Initial Revision (SM / TP)
//    -19 OCT 2006
//


//-----------------------------------------------------------------------------
// 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;                     // 10-bit ADC0 result

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

#define SYSCLK        24500000         // SYSCLK frequency in Hz
#define BAUDRATE      115200           // Baud rate of UART in bps
#define ANALOG_INPUTS 6                // Number of AIN pins to measure,
                                       // skipping the UART0 pins
#define INT_DEC       256              // Integrate and decimate ratio

#define TIMER0_RELOAD_HIGH  0          // Timer0 High register
#define TIMER0_RELOAD_LOW 255          // Timer0 Low register

//-----------------------------------------------------------------------------
// Function PROTOTYPES
//-----------------------------------------------------------------------------

void Oscillator_Init (void);
void Port_Init (void);
void Timer2_Init(void);
void ADC0_Init(void);
void UART0_Init (void);

void Timer0_wait(int ms);

//-----------------------------------------------------------------------------
// Global Variables
//-----------------------------------------------------------------------------

long RESULT[ANALOG_INPUTS];            // ADC0 decimated value, one for each
                                       // analog input

// Port1 ADC Inputs
unsigned char idata PIN_TABLE[ANALOG_INPUTS] = {0,1,2,3,4,5};

unsigned char AMUX_INPUT = 0;          // Index of analog MUX inputs

//-----------------------------------------------------------------------------
// MAIN Routine
//-----------------------------------------------------------------------------
void main (void)
{
   unsigned char i;
   unsigned long measurement;

   PCA0MD &= ~0x40;                    // WDTE = 0 (clear watchdog timer
                                       // enable)

   Oscillator_Init ();                 // Initialize system clock to
                                       // 24.5MHz
   Port_Init ();                       // Initialize crossbar and GPIO
   Timer2_Init();                      // Init Timer2 to generate
                                       // overflows to trigger ADC
   UART0_Init();                       // Initialize UART0 for printf's
   ADC0_Init();                        // Initialize ADC0

   EA = 1;                             // Enable global interrupts
   while (1)
   {
      EA = 0;                          // Disable interrupts
      printf("\f");
      for(i = 0; i < ANALOG_INPUTS; i++)
      {
         // The 10-bit ADC value is averaged across INT_DEC measurements.
         // The result is then stored in RESULT, and is right-justified
         // The measured voltage applied to the port pins is then:
         //
         //                           Vref (mV)
         //   measurement (mV) =   --------------- * Result (bits)
         //                        (2^10)-1 (bits)

         measurement =  (RESULT[i] - 8) * 3268 / 1023;
         printf("P1.%bu voltage: %4ld mV\n",PIN_TABLE[i],measurement);
      }
      EA = 1;                          // Re-enable interrupts

      Timer0_wait(25);                 // Wait before displaying new values
   }
}

//-----------------------------------------------------------------------------
// Initialization Subroutines
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// SYSCLK_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine initializes the system clock to use the internal 24.5MHz
// oscillator as its clock source.  Also enables missing clock detector reset.
//
//-----------------------------------------------------------------------------
void Oscillator_Init (void)
{
   OSCICN = 0x83;                      // Configure internal oscillator for
                                       // its highest frequency
   RSTSRC = 0x04;                      // Enable missing clock detector
}

//-----------------------------------------------------------------------------
// Port_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// Configure the Crossbar and GPIO ports.
//