f500_adc0_externalinput_mux.c

C8051F500开发编程：MCU全部资源应用实例

//-----------------------------------------------------------------------------
// F500_ADC0_ExternalInput_Mux.c
//-----------------------------------------------------------------------------
// Copyright 2008 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 1 (P2.0), 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 MHz 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 P2.0.  <ANALOG_INPUTS>
// inputs are read.  The amplifier is set for 0.44 gain so a voltage range of
// 0 to 5V (2.2V) may be measured.  Although voltages up to 5V 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| P2.x     |  |
//         o|    |        |
//         o|     --------
//         o|
//         o|
//         o|
//          |
// ---------
//
// How To Test:
//
// 1) Download code to a 'F500 device that is connected to a UART transceiver
// 2) Verify the TX and RX jumpers are populated on J17.
// 3) Connect USB cable from the development board to a PC
// 4) On the PC, open HyperTerminal (or any other terminal program) and connect
//    to the USB port (virtual com port) at <BAUDRATE>, 8 data bits, no parity,
//    1 stop bit and no flow control.
// 5) 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:         C8051F500 (Side A of a C8051F500-TB)
// Tool chain:     Keil C51 8.0 / Keil EVAL C51
// Command Line:   None
//
// Release 1.1 / 10 JUN 2008 (ADT)
//    -Edited formatting
//
// Release 1.0 / 03 MAR 2008 (GP)
//    -Initial Revision
//


//-----------------------------------------------------------------------------
// Includes
//-----------------------------------------------------------------------------

#include <compiler_defs.h>
#include <C8051F500_defs.h>            // SFR declarations
#include <stdio.h>

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

#define SYSCLK         24000000        // SYSCLK frequency in Hz
#define BAUDRATE         115200        // Baud rate of UART in bps
#define ANALOG_INPUTS         8        // 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);

INTERRUPT_PROTO (ADC_ISR, INTERRUPT_ADC0_EOC);
INTERRUPT_PROTO (TIMER2_ISR, INTERRUPT_TIMER2);

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

// ADC0 decimated value, one for each analog input
SEGMENT_VARIABLE (RESULT[ANALOG_INPUTS], U32, xdata);       

// ADC0 input matrix.  Bit-wise OR with 0x10 to get the ADC0MX setting for P2
U8 PIN_TABLE[ANALOG_INPUTS] = { 0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07 };

U8 AMUX_INPUT = 0;          // Index of analog MUX inputs

// Integrate accumulator for the ADC samples from input pins
U32 accumulator[ANALOG_INPUTS];

//-----------------------------------------------------------------------------
// MAIN Routine
//-----------------------------------------------------------------------------
void main (void)
{
   U8  i;                              // Loop counter
   U32 measurement;                    // Voltage measurement

   SFRPAGE = ACTIVE_PAGE;              // Set for PCA0MD and for printf()

   PCA0MD &= ~0x40;                    // Disable the watchdog timer

   OSCILLATOR_Init ();                 // Initialize system clock
   PORT_Init ();                       // Initialize crossbar and GPIO
   TIMER2_Init ();                     // Init Timer2 to trigger ADC
   UART0_Init ();                      // Initialize UART0 for printf's
   ADC0_Init ();                       // Initialize ADC0

   // Initialize global variable
   for (i = 0; i < ANALOG_INPUTS; i++) 
   {
      accumulator[i] = 0; 
   }

   EA = 1;                             // Enable global interrupts

   while (1)
   {
      EA = 0;                          // Disable interrupts
      printf ("\f");
      for (i = 0; i < ANALOG_INPUTS; i++)
      { 
         // The 12-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)
         //                        (2^12)-1 (bits)
         //
         // Then multiply the result by 2.27 to account for the 0.44 gain
         // applied earlier

         measurement =  RESULT[i] * 2400 / 4096 * 227 / 100;
         printf("P2.%bu voltage: %4ld mV\n", PIN_TABLE[i], measurement);
      }
      EA = 1;                          // Re-enable interrupts

      Timer0_wait(20);                 // Wait before displaying new values
   }
}

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

//-----------------------------------------------------------------------------
// OSCILLATOR_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine initializes the system clock to use the internal 24 MHz
// oscillator as its clock source.  Also enables missing clock detector reset.
//
//-----------------------------------------------------------------------------
void OSCILLATOR_Init (void)
{
   U8 SFRPAGE_save = SFRPAGE;
   SFRPAGE = CONFIG_PAGE;

   OSCICN = 0x87;                      // Configure internal oscillator for
                                       // its highest frequency
   RSTSRC = 0x04;                      // Enable missing clock detector

   SFRPAGE = SFRPAGE_save;
}

//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
//
// Return Value:  None
// Parameters:    None
//
// Configure the Crossbar and GPIO ports.
//
// P0.0 -          analog               VREF
// P0.4 -          digital  push-pull   UART TX
// P0.5 -          digital  open-drain  UART RX
//
// P1.3 -          digital  push-pull   LED
//
// P2.0 - P2.7     analog               ADC inputs
//
//-----------------------------------------------------------------------------
void PORT_Init (void)
{
   U8 SFRPAGE_save = SFRPAGE;
   SFRPAGE = CONFIG_PAGE;

   P0SKIP  |= 0x01;                    // Skip P0.0 (VREF)
   P0MDOUT |= 0x10;                    // Set TX pin to push-pull
   P0MDIN  &= ~0x01;                   // Set VREF to analog

   P1MDOUT |= 0x08;                    // Enable LED as a push-pull output

   P2SKIP  = 0xFF;                     // Skip all of P2 for analog inputs
   P2MDIN  = 0x00;                     // Configure all of P2 as analog inputs

   XBR0     = 0x01;                    // Enable UART0