f00x_pca0_capture_input.c

芯科原厂所有c8051fxx程序的例子。

//-----------------------------------------------------------------------------
// F00x_PCA0_Capture_Input.c
//-----------------------------------------------------------------------------
// Copyright 2006 Silicon Laboratories, Inc.
// http://www.silabs.com
//
// Program Description:
//
// This program uses the PCA's capture mode to time events on an input pin.
// The difference between subsequent captures is calculated and stored in
// memory.
//
// In this example, PCA Module 0 is used to capture rising edges of an
// incoming digital waveform, and the crossbar is configured to receive the
// CEX0 pin on on P0.0.  The PCA is configured to clock once every 10 us.
//
// Timer2 overflows are used to toggle pin P0.1 at an overflow rate specified
// by the definition T2_RELOAD_CLOCKS. This signal at P0.1 is provided simply
// as a test method for the code.
//
// How To Test:
//
// 1) Download code to a 'F00x device with P0.0 and P0.1 tied together.
// 2) Run the program for a few seconds, and then halt.
// 3) Verify that the variable "capture_period" is equal to 50 (=500us).
//
// Alternately:
// 1) Run a separate signal generator into the P0.0 pin.
// 2) Run the program for a few seconds, and then halt.
// 3) Verify that the variable "capture_period" matches the expected time
//    between rising edges (in units of 10us).
//
//
// FID:            00X000024
// Target:         C8051F00x
// Tool chain:     Keil C51 8.00 / Keil EVAL C51
// Command Line:   None
//
//
// Release 1.0
//    -Initial Revision (BD)
//    -22 AUG 2006
//


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

#include <c8051f000.h>                 // SFR declarations


//-----------------------------------------------------------------------------
// Global Constants
//-----------------------------------------------------------------------------

#define SYSCLK       22118400          // External oscillator frequency in Hz

#define T0_CLOCKS 221                  // Use 221 clocks per T0 Overflow
                                       //    (221 ~= 10 us)
#define T2_RELOAD_CLOCKS 5525          // SYSCLKs per 1/2 cycle square wave
                                       //    (221 ~= 10 us)

sfr16 RCAP2 = 0xCA;                    // Timer2 Reload Register
sfr16 TMR2 = 0xCC;                     // Timer2 counter

sbit TEST_OUT = P0^1;                  // Output for testing purposes

//-----------------------------------------------------------------------------
// Function Prototypes
//-----------------------------------------------------------------------------

void OSCILLATOR_Init (void);
void PORT_Init (void);
void PCA0_Init (void);

void TestTimerInit (void);

//-----------------------------------------------------------------------------
// main() Routine
//-----------------------------------------------------------------------------

void main (void)
{
   // Disable watchdog timer
   WDTCN = 0xde;
   WDTCN = 0xad;

   PORT_Init ();                       // Initialize crossbar and GPIO
   OSCILLATOR_Init ();                 // Initialize oscillator
   PCA0_Init ();                       // Initialize PCA0

   TestTimerInit ();                   // Configure Timer2 for test signal

   EA = 1;

   while (1)
   {
      // check to see if Timer2 overflowed
      if (TF2)
      {
         TEST_OUT = ~TEST_OUT;         // Toggle test pin
         TF2 = 0;                      // Clear T2 overflow
      }

   };
}


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

//-----------------------------------------------------------------------------
// OSCILLATOR_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This function initializes the system clock to use the external crystal
// oscillator with a crystal of 22.1184 MHz.
//
//-----------------------------------------------------------------------------
void OSCILLATOR_Init (void)
{
   int i;                              // Delay counter

   OSCXCN = 0x67;                      // Start external oscillator with
                                       // 22.1184MHz crystal

   for (i=0; i < 256; i++) ;           // Wait for oscillator to start

   while (!(OSCXCN & 0x80)) ;          // Wait for crystal osc. to settle

   OSCICN = 0x88;                      // Select external oscillator as SYSCLK
                                       // source and enable missing clock
                                       // detector
}

//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This function configures the crossbar and GPIO ports.
//
// P0.0   digital   open-drain     PCA0 CEX0
// P0.1   digital   push-pull
//
//-----------------------------------------------------------------------------
void PORT_Init (void)
{
   XBR0    = 0x08;                     // Route CEX0 to P0.0
   XBR1    = 0x00;
   XBR2    = 0x40;                     // Enable crossbar and weak pull-ups

   PRT0CF |= 0x02;                     // Set TEST_OUT (P0.1) to push-pull
}

//-----------------------------------------------------------------------------
// PCA0_Init
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This function configures the PCA time base, and sets up capture mode for
// Module 0 (CEX0 pin).
//
// The PCA will capture rising edges on the CEX0 pin, and interrupt the
// processor.  Software subtracts the previous capture value from the most
// recent caputre value to set the "captured_clocks" variable.
//
// The PCA time base in this example is configured to use Timer 0, overflowing
// about every 10 us. The PCA clock rate will determine the maximum time
// between edges that can be reliably detected (this is equal to 65535 * the
// PCA clock).
//
// The time range that can be measured using this example is ~10us (MIN) to
// ~655.350 ms (MAX) when the clocks are set up as they are in this example.
// The precision is limited to the PCA clock rate (in this example, ~10 us).
// Using different PCA clock sources or a different processor clock will allow
// for different time capture ranges or levels of precision.
//
//    -------------------------------------------------------------------------
//    How "Capture Mode" Works:
//
//    The PCA's Capture Mode works by making a copy of the current PCA timer
//    value (PCA0) into the capture/compare register for the module (PCA0CPn).
//    The module can be configured to capture rising edges, falling edges, or
//    both rising and falling edges.  When a capture occurs, the CCFn flag is
//    set, and an interrupt is (optionally) generated by the PCA module.
//
//    To detect an edge (and not reject it as noise) the new logic level must
//    be present at the pin for at least two SYSCLK cycles.
//
//    With a constantly-running PCA timer, the time between two edges on a
//    signal can be accurately measured to within 1 PCA clock cycle.
//    Multiple PCA channels can be used in capture mode to measure timing
//    between different signals.
//    -------------------------------------------------------------------------
//
//-----------------------------------------------------------------------------
void PCA0_Init (void)
{
   // Configure Timer 0 for 8-bit auto-reload mode, using SYSCLK as time base
   TMOD &= 0xF0;                       // Clear all T0 control bits
   TMOD |= 0x02;                       // 8-bit auto-reload timer
   CKCON |= 0x08;                      // T0 uses SYSCLK
   TH0 = -T0_CLOCKS;                   // Set up reload value
   TL0 = -T0_CLOCKS;                   // Set up initial value

   // Configure PCA time base; overflow interrupt disabled
   PCA0CN = 0x00;                      // Stop counter; clear all flags
   PCA0MD = 0x04;                      // Use Timer 0 as time base


   PCA0CPM0 = 0x21;                    // Module 0 = Rising Edge Capture Mode
                                       // enable CCF flag.


   EIE1 |= 0x08;                       // Enable PCA interrupts

   // Start PCA counter
   CR = 1;
   TR0 = 1;                            // Start Timer 0
}


//-----------------------------------------------------------------------------
// TestTimerInit
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine simply sets up Timer 2 in 16-bit auto-reload mode, to be used
// as a rudimentary source for testing
//
// The T2_RELOAD_CLOCKS value can be set up to generate multiples of 10us for
// testing, by using the formula:
//
// T2_RELOAD_CLOCKS = 221 * (Time_between_rising_edges / 10us)/2
//
//-----------------------------------------------------------------------------
void TestTimerInit (void)
{

   CKCON |= 0x20;                      // Use SYSCLK to clock Timer2

   RCAP2 = -(int)T2_RELOAD_CLOCKS;     // Set up Timer 2 reload rate
   TMR2 = -(int)T2_RELOAD_CLOCKS;      // Preload timer

   T2CON = 0x04;                       // Timer 2 run in 16b auto-reload

}


//-----------------------------------------------------------------------------
// Interrupt Service Routines
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// PCA0_ISR
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This is the ISR for the PCA.  It handles the case when a capture occurs on
// channel 0, and updates the variables to reflect the new capture information.
//
//-----------------------------------------------------------------------------
void PCA0_ISR (void) interrupt 9
{
   static unsigned int current_capture_value, previous_capture_value;
   static unsigned int capture_period;


   if (CCF0)                           // If Module 0 caused the interrupt
   {
      CCF0 = 0;                        // Clear module 0 interrupt flag.

      // Store most recent capture value
      current_capture_value = (PCA0CPH0 << 8) | PCA0CPL0;

      // Calculate capture period from last two values.
      capture_period = current_capture_value - previous_capture_value;

      // Update previous capture value with most recent info.
      previous_capture_value = current_capture_value;

   }
   else                                // Interrupt was caused by other bits.
   {
      PCA0CN &= ~0x86;                 // Clear other interrupt flags for PCA
   }
}

//-----------------------------------------------------------------------------
// End Of File
//-----------------------------------------------------------------------------