C8051F320_ADC.rar_C8051F320 A_c8051f320_c8051f320 a_c8051f320 A

//----------------------------------------------------------------------------- // F32x_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 12MHz 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 'F32x 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. // // FID: 32X000091 // Target: C8051F32x // Tool chain: Keil C51 7.50 / Keil EVAL C51 // Command Line: None // // Release 1.0 // -Initial Revision (SM / TP) // -19 OCT 2006 // //----------------------------------------------------------------------------- // Includes //----------------------------------------------------------------------------- #include <C8051F320.h> // SFR declarations #include <stdio.h> //----------------------------------------------------------------------------- // 16-bit SFR Definitions for 'F32x //----------------------------------------------------------------------------- sfr16 TMR2RL = 0xCA; // Timer2 reload value sfr16 TMR2 = 0xCC; // Timer2 counter sfr16 ADC0 = 0xBD; // 10-bit ADC0 result //----------------------------------------------------------------------------- // Global CONSTANTS //----------------------------------------------------------------------------- #define SYSCLK 12000000 // 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 // 12MHz Port_Init (); // Initialize crossbar and GPIO Timer2_Init(); // Init Timer2 to generate // overflows to trigger ADC UART0_Init(); // Initialize UART0 for pri