//-----------------------------------------------------------------------------
// F41x_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
// P1.1 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 P1.1 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
// VREF and AGND on the terminal strip as shown below:
//
// ---------
// |
// o| VREF ----|
// o| GND ---|<-|
// o| P1.1 | |
// o| | |
// o| --------
// o|
// |
//----------
// C8051F410-TB
//
// 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 change the mux input and start a conversion
// every 100uS, which is far longer than the minimum required.
//
// F41x Resources:
// ---------------
// Timer1: clocks UART
// Timer2: overflow initiates ADC conversion
//
//
// How To Test:
// ------------
// 1) Download code to a 'F410 device on a C8051F410-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 Vref)
// to P1.1, or a potentiometer voltage divider as shown above.
// 5) HyperTerminal will print the voltage measured by the device if
// everything is working properly
//
// FID: 41X000030
// Target: C8051F410
// Tool chain: Raisonance / Keil
// Command Line: None
//
// Release 1.1 / 11 MAR 2010 (GP)
// -Tested with Raisonance
//
// Release 1.0
// -SM
// -26-July-06
//-----------------------------------------------------------------------------
// Includes
//-----------------------------------------------------------------------------
#include <compiler_defs.h>
#include <C8051F410_defs.h> // SFR declarations
#include <stdio.h>
//-----------------------------------------------------------------------------
// Global CONSTANTS
//-----------------------------------------------------------------------------
#define SYSCLK 24500000 // SYSCLK frequency in Hz
#define BAUDRATE 9600//115200 // Baud rate of UART in bps
sbit LED = P1^3; // LED='1' means ON
sbit COMM = P0^7;
sbit DCin= P2^0;
//-----------------------------------------------------------------------------
// Function PROTOTYPES
//-----------------------------------------------------------------------------
void SYSCLK_Init (void);
void PORT_Init (void);
void Timer2_Init(void);
void ADC0_Init(void);
void UART0_Init (void);
//-----------------------------------------------------------------------------
// MAIN Routine
//-----------------------------------------------------------------------------
void main (void)
{
PCA0MD &= ~0x40; // WDTE = 0 (clear watchdog timer
// enable)
COMM=1;
DCin=0;
SYSCLK_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) { // spin forever
}
}
//-----------------------------------------------------------------------------
// 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 SYSCLK_Init (void)
{
OSCICN = 0x87; // configure internal oscillator for
// 24.5MHz
RSTSRC = 0x04; // enable missing clock detector
}
//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Configure the Crossbar and GPIO ports.
// P0.4 - UART TX (push-pull)
// P0.5 - UART RX
// P1.1 - ADC0 analog input
// P1.3 - LED (push-pull)
//
//-----------------------------------------------------------------------------
void PORT_Init (void)
{
XBR0 = 0x01; // Enable UART0
XBR1 = 0x40; // Enable crossbar and weak pull-ups
P0MDOUT |= 0x10; // Set TX pin to push-pull
P1MDOUT |= 0x08; // enable LED as a push-pull output
P1MDIN &= 0xEF; // set P1.4 as an analog input
P1SKIP |= 0x10; // skip P1.4 pin
}
//-----------------------------------------------------------------------------
// Timer2_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Configure Timer2 to 16-bit auto-reload and generate an interrupt at 100uS
// intervals. Timer 2 overflow automatically triggers ADC0 conversion.
//
//-----------------------------------------------------------------------------
void Timer2_Init (void)
{
TMR2CN = 0x00; // Stop Timer2; Clear TF2;
// use SYSCLK as timebase, 16-bit
// auto-reload
CKCON = 0x30; // select SYSCLK for timer 2 source
TMR2RL = - (SYSCLK / 1000); // init reload value for 10uS
TMR2 = 0xffff; // set to reload immediately
TR2 = 1; // start Timer2
}
//-----------------------------------------------------------------------------
// ADC0_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Configures ADC0 to make single-ended analog measurements on pin P1.4
//
//-----------------------------------------------------------------------------
void ADC0_Init (void)
{
ADC0CN = 0x03; // ADC0 disabled, normal tracking,
// conversion triggered on TMR2 overflow
REF0CN = 0x0A; // Enable on-chip VREF = 2.2v and buffer
ADC0MX = 0x0C; // Set P1.4 as positive input
ADC0CF = ((SYSCLK/3000000)-1)<<3; // set SAR clock to 3MHz
ADC0CF |= 0x00; // right-justify results
EIE1 |= 0x08; // enable ADC0 conversion complete int.
AD0EN = 1; // enable ADC0
}
//-----------------------------------------------------------------------------
// UART0_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Configure the UART0 using Timer1, for <BAUDRATE> and 8-N-1.
//
//-----------------------------------------------------------------------------
void UART0_Init (void)
{
SCON0 = 0x10; // SCON0: 8-bit variable bit rate
// level of STOP bit is ignored
// RX enabled
// ninth bits are zeros
// clear RI0 and TI0 bits
if (SYSCLK/BAUDRATE/2/256 < 1) {
TH1 = -(SYSCLK/BAUDRATE/2);
CKCON |= 0x08; // T1M = 1; SCA1:0 = xx
} else if (SYSCLK/BAUDRATE/2/256 < 4) {
TH1 = -(SYSCLK/BAUDRATE/2/4);
CKCON &= ~0x0B; // T1M = 0; SCA1:0 = 01
CKCON |= 0x01;
} else if (SYSCLK/BAUDRATE/2/256 < 12) {
TH1 = -(SYSCLK/BAUDRATE/2/12);
CKCON &= ~0x0B; // T1M = 0; SCA1:0 = 00
} else if (SYSCLK/BAUDRATE/2/256 < 48) {
TH1 = -(SYSCLK/BAUDRATE/2/48);
CKCON &= ~0x0B; // T1M = 0; SCA1:0 = 10
CKCON |= 0x02;
} else {
while (1); // Error. Unsupported baud rate
}
TL1 = TH1; // init Timer1
TMOD &= ~0xf0; // TMOD: timer 1 in 8-bit autoreload
TMOD |= 0x20;
TR1 = 1; // START Timer1
TI0 = 1; // Indicate TX0 ready
}
//-----------------------------------------------------------------------------
// Interrupt Service Routines
//-----------------------------------------------------------------------------
//
//-----------------------------------------------------------------------------
// ADC0_ISR
//-----------------------------------------------------------------------------
//
// This ISR averages 2048 samples then prints the result to the terminal. The
// ISR is called after each ADC conversion which is triggered by Timer2.
//
//-----------------------------------------------------------------------------
void ADC0_ISR (void) interrupt 10
{
static unsigned long accumulator = 0; // accumulator for averaging
static unsigned int measurements = 2048; // measurement counter
unsigned long result=0;
unsigned long mV; // measured voltage in mV
AD0INT = 0; // clear ADC0 conv. complete flag
accumulator += ADC0;
measurements--;
if(measurements == 0)
{
measurements = 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)
// (2^12)-1 (bits)
mV = result * 2500 / 4095;
printf("P1.4voltage Voltage: %ld mV\n",mV);
}
}
//-----------------------------------------------------------------------------
// End Of File
//-----------------------------------------------------------------------------
代码如上，我每次用电压表测到的电压与程序返回的电压误差大概再200MV左右，会不会是外部电路的问题？？REF0CN选择了VDD为电压基准源，VDD为2.5V，另外将REF0CN设置用VDD作为电压基准源之后，就会自动忽略VREF的吧，我的电路里VREF接在了VCC 5V电压上，这个会不会影响到ADC模块？ |
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