有關C8051F410 ADC的問題
想請教使用ADC的問題,就是我使用P1.6輸入一組類比訊號,再用ADC去取值,
發現當我啟動ADC去取值時,類比訊號隨著ADC的動作會有100mv大小的noise
產生,理論上ADC應該不會影響輸入訊號才對,不知有什麼要注意的地方呢?
謝謝大家
程式片段如下:
void PORT_Init (void)
{
// P0.0 - Unassigned, Open-Drain, Digital
// P0.1 - Unassigned, Open-Drain, Digital
// P0.2 - Unassigned, Open-Drain, Digital
// P0.3 - Unassigned, Open-Drain, Digital
// P0.4 - TX0 (UART0), Push-Pull, Digital
// P0.5 - RX0 (UART0), Open-Drain, Digital
// P0.6 - Unassigned, Open-Drain, Digital
// P0.7 - Unassigned, Open-Drain, Digital
// P1.0 - Unassigned, Open-Drain, Digital
// P1.1 - Unassigned, Open-Drain, Digital
// P1.2 - Unassigned, Open-Drain, Digital
// P1.3 - Unassigned, Open-Drain, Digital
// P1.4 - Unassigned, Open-Drain, Digital
// P1.5 - Unassigned, Open-Drain, Digital
// P1.6 - Skipped, Open-Drain, Analog
// P1.7 - Unassigned, Open-Drain, Digital
// P2.0 - Unassigned, Open-Drain, Digital
// P2.1 - Unassigned, Open-Drain, Digital
// P2.2 - Unassigned, Open-Drain, Digital
// P2.3 - Unassigned, Open-Drain, Digital
// P2.4 - Unassigned, Open-Drain, Digital
// P2.5 - Unassigned, Open-Drain, Digital
// P2.6 - Unassigned, Open-Drain, Digital
// P2.7 - Unassigned, Open-Drain, Digital
P1MDIN = 0xBF;
P0MDOUT = 0x10;
P1SKIP = 0x40;
XBR0 = 0x01; // No digital peripherals selected
}
//-----------------------------------------------------------------------------
//ADC Init
//-----------------------------------------------------------------------------
void ADC_Init(void)
{
ADC0MX = 0x0E; // P1.6 selected at + input
ADC0CN = 0x80;
ADC0TK = 0xF7;
ADC0CF = (SYSCLK/715000) << 3;
REF0CN = 0x09; // disable temp sensor, VREF = VDD(2.5v),
EIE1 &= ~0x08; // Disable ADC0 EOC interrupt
}
//-----------------------------------------------------------------------------
//ADC measure
//-----------------------------------------------------------------------------
unsigned int measure (void)
{
unsigned i; // Sample counter
unsigned long accumulator=0L; // Here's where we integrate the
// ADC samples
unsigned int currval;
AD0INT = 0;
AD0BUSY = 1;
i = 0;
do
{
while (!AD0INT); // Wait for conversion to complete
AD0INT = 0; // Clear end-of-conversion indicator
currval= ADC0H << 8 | ADC0L; // Store latest ADC conversion
AD0BUSY = 1; // Initiate conversion
accumulator += currval; // Accumulate
i++; // Update counter
} while (i != AVG_TIMES);
return (unsigned int) (accumulator/AVG_TIMES);
}
