C8051F340的ADC差分输入测量值偏小是怎么回事？
先说一下情况：单端测量的时候，即P1.1作为输入的时候，测量是准确的
差分测量的时候，P1.1是AIN+，P1.2是AIN-， P1.1 = 2V，P1.2 = 1V
测量结果mv = 498mv
测量条件：
参考电压是内部参考电压=2.44V，SAR CLOCK = 3MHZ，采用内部时钟=12MHZ
请帮忙看一下程序，是哪里出问题了呢？
主要是看ADC初始化和ADC中断函数
程序如下：
//-----------------------------------------------------------------------------
// Includes
//-----------------------------------------------------------------------------
#include "c8051F340.h" // SFR declarations
#include <stdio.h>
//-----------------------------------------------------------------------------
// 16-bit SFR Definitions for 'F34x
//-----------------------------------------------------------------------------
sfr16 TMR2RL = 0xca; // Timer2 reload value
sfr16 TMR2 = 0xcc; // Timer2 counter
sfr16 ADC0 = 0xbd; // ADC0 result
//-----------------------------------------------------------------------------
// Global CONSTANTS
//-----------------------------------------------------------------------------
#define SYSCLK 12000000 // SYSCLK frequency in Hz
#define BAUDRATE 115200 // Baud rate of UART in bps
sbit LED = P2^2; // 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);
//-----------------------------------------------------------------------------
// MAIN Routine
//-----------------------------------------------------------------------------
void main (void)
{
PCA0MD &= ~0x40; // WDTE = 0 (clear watchdog timer
// enable)
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 12MHz
// oscillator as its clock source.Also enables missing clock detector reset.
//
//-----------------------------------------------------------------------------
void SYSCLK_Init (void)
{
OSCICN = 0x83; // configure internal oscillator for
// 12MHz / 1
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
// P2.2 - 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
P2MDOUT |= 0x04; // enable LED as a push-pull output
P1MDIN &= ~0x06; // set P1.1 as an analog input
P1SKIP&= ~0x06; //datasheet上说要skip
}
//-----------------------------------------------------------------------------
// 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|= 0x10; // select SYSCLK for timer 2 source
TMR2RL= 65535 - (SYSCLK / 10000); // init reload value for 100uS
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 P1.1
//
//-----------------------------------------------------------------------------
void ADC0_Init (void)
{
ADC0CN = 0x02; // ADC0 disabled, normal tracking,
// conversion triggered on TMR2 overflow
REF0CN = 0x03; // Enable on-chip VREF and buffer
AMX0P = 0x13; // ADC0 positive input = P1.1
AMX0N = 0x14; // ADC0 negative input = P1.2
//Differential mode
ADC0CF = ((SYSCLK/3000000)-1)<<3; // set SAR clock to 3MHz
ADC0CF &= ~0x04; // 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
{
staticlong 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)
// (2^10)-1 (bits)
mV =result * 2440 / 1023;
printf("P1.1 voltage: %ld mV\n",mV);
}
LED=~LED; // Toggle LED
}
居然没有人看，还是我自己孤芳自赏吧
问题已解决：
百度问题的时候，看到网页上说结果是以二进制的补码形式保存的，于是重新看了一下DATASHEET，发现果然如此，又奇妙的发现当差分输入的时候，测量范围是VREF~VREF*511/512,后面也有对应的示例ADC的值，发现在计算实际电压值的时候，应当是除以512而不是1023，一运行，果然如此。
心情从此晴朗 新华龙51片子性价比太低了，用ARM吧 yufeistudio 发表于 2015-3-22 19:11
新华龙51片子性价比太低了，用ARM吧
ARM还没学过，现在一直在用C8051F系列的单片机，等有机会就接触一下ARM LZ你好，我也在用F340，由于论坛等级限制，不能发消息，留个联系方式，大家互相交流下。 sos9616 发表于 2015-5-5 11:27
LZ你好，我也在用F340，由于论坛等级限制，不能发消息，留个联系方式，大家互相交流下。 ...
QQ： 1093699313 山风 新龙华的单片机我也刚接触，感觉不怎么地。。。。 过去好久，忘了来这里说明一下原因了。
问题出在差分输入和单端输入的差别上，单端输入的时候mV =result * 2440 / 1023;但差分输入的时候，mV =result * 2440 / 512;（或是/511）。
这个是在查数据手册的时候看到的，单端输入的最大输入值是VREF*1023/1024，差分输入的最大值是VREF*511/512，再算一算上面给的例子，得出的结果就是上一行所说的。
在英文数据手册的第42页 魏道志 发表于 2015-5-5 16:28
新龙华的单片机我也刚接触，感觉不怎么地。。。。
还不熟悉的原因，比传统的51强多了，别的不说，就说在线调试这一点，就非常方便 deyu35 发表于 2015-5-6 08:38
还不熟悉的原因，比传统的51强多了，别的不说，就说在线调试这一点，就非常方便 ...
恩恩，就是性价比不高，大家现在都用ARM，，，我也不明白公司为什么用新龙华这款 c8051f 混合信号做的还是不错的就是性价比差 楼主说的二进制补码是什么情况？，新手求指导，我用开发板的测试程序ADC串口输出可以，想用屏12864显示就不行
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