// Program Description:
//
// This program helps the user to learn about operating the Watch Dog Timer.
// The WDT is used to generate resets if the times between writes to the WDT
// update register (PCA0CPH5) exceed a specified limit. The WDT can be disabled
// and enabled in the software as needed. When enabled the PCA Module 5 acts as
// the WDT. This program resets the MCU when P1.4 switch is pressed. Also upon
// reset the LED blinks approximately five times faster when compared to
// before.The reset is caused due to a WDT overflow and can be confirmed by
// checking the value of the RSTSRC register where bit 3 is set to indicate a
// reset caused by WDT.
//
// Resources Used:
// * Internal Oscillator: MCU clock source
// * Timer 2: Blinks LED
// * PCA Module 5 : Watchdog Timer
//
// How to Test:
// 1) Compile and download code to a 'F500 device.
// 2) Make sure the LED and switch jumpers are placed on J19.
// 3) Run the code:
// - The test will blink the LED at a rate of 10Hz until the switch SW1
// (P1.4) is pressed.
// - Once the the switch is pressed and held for a long enough time,
// it will prevent the WDT from being touched and the WDT will
// cause a reset.
// - Upon reset the code checks for a WDT reset and blinks the LED five
// times faster than before to indicate the same.
//
// Target: C8051F500 (Side A of a C8051F500-TB)
// Tool chain: Keil C51 8.0 / Keil EVAL C51
// Command Line: None
//
// Release 1.1 / 11 JUN 2008 (ADT)
// -Edited Formatting
//
// Release 1.0 / 03 MAR 2008 (GP)
// -Initial Revision
//
//-----------------------------------------------------------------------------
// Includes
//-----------------------------------------------------------------------------
#include <compiler_defs.h>
#include <C8051F500_defs.h> // SFR declarations
//-----------------------------------------------------------------------------
// Global CONSTANTS
//-----------------------------------------------------------------------------
#define SYSCLK 24000000 / 8 // SYSCLK frequency in Hz
SBIT (LED, SFR_P1, 3); // LED == 1 means ON
SBIT (SW1, SFR_P1, 4); // SW1 == 0 means switch depressed
//-----------------------------------------------------------------------------
// Function PROTOTYPES
//-----------------------------------------------------------------------------
void OSCILLATOR_Init (void);
void PORT_Init (void);
void PCA_Init (void);
void TIMER2_Init (U16 counts);
INTERRUPT_PROTO (TIMER2_ISR, INTERRUPT_TIMER2);
//-----------------------------------------------------------------------------
// main() Routine
//-----------------------------------------------------------------------------
//
// The MAIN routine performs all the intialization, and then loops until the
// switch is pressed. When SW2 (P0.7) is pressed the code checks the RSTSRC
// register to make sure if the last reset is because of WDT.
//-----------------------------------------------------------------------------
void main (void)
{
SFRPAGE = ACTIVE_PAGE; // Set SFR Page for PCA0MD and RSTSRC
PCA0MD &= ~0x40; // Disable the watchdog timer
OSCILLATOR_Init (); // Initialize system clock to 24.5/8 MHz
PCA_Init (); // Intialize the PCA
PORT_Init (); // Initialize crossbar and GPIO
if ((RSTSRC & 0x02) == 0x00) // First check the PORSF bit. if PORSF
{ // is set, all other RSTSRC flags are
// invalid
// Check if the last reset was due to the Watch Dog Timer
if (RSTSRC == 0x08)
{
TIMER2_Init (SYSCLK / 12 / 50); // Make LED blink at 50Hz
EA = 1; // Enable global interrupts
while (1); // Wait forever
}
else
{
// Init Timer2 to generate interrupts at a 10Hz rate.
TIMER2_Init (SYSCLK / 12 / 10);
}
}
// Calculate Watchdog Timer Timeout
// Offset calculated in PCA clocks
// Offset = ( 256 x PCA0CPL5 ) + 256 - PCA0L
// = ( 256 x 255(0xFF)) + 256 - 0
// Time = Offset * (12/SYSCLK)
// = 255 ms ( PCA uses SYSCLK/12 as its clock source)
PCA0MD &= ~0x40; // Disable watchdog timer
PCA0L = 0x00; // Set lower byte of PCA counter to 0
PCA0H = 0x00; // Set higher byte of PCA counter to 0
PCA0CPL5 = 0xFF; // Write offset for the WDT
PCA0MD |= 0x40; // Enable the WDT
EA = 1; // Enable global interrupts
//--------------------------------------------------------------------------
// Main Application Loop/Task Scheduler
//--------------------------------------------------------------------------
while (1)
{
//----------------------------------------------------------------------
// Task #1 - Check Port I/O
//----------------------------------------------------------------------
while (!SW1); // Force the MCU to stay in this task as
// long as SW1 is pressed. This task must
// finish before the watchdog timer
// timeout expires.
//----------------------------------------------------------------------
// Task #2 - Reset Watchdog Timer
//----------------------------------------------------------------------
PCA0CPH5 = 0x00; // Write a 'dummy' value to the PCA0CPH5
// register to reset the watchdog timer
// timeout. If a delay longer than the
// watchdog timer delay occurs between
// successive writes to this register,
// the device will be reset by the watch
// dog timer.
}
}
//-----------------------------------------------------------------------------
// Initialization Subroutines
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
// OSCILLATOR_Init
//-----------------------------------------------------------------------------
// Return Value : None
// Parameters : None
//
// This routine initializes the system clock to use the internal 24 MHz / 8
// oscillator as its clock source. Also enables missing clock detector reset.
//-----------------------------------------------------------------------------
void OSCILLATOR_Init (void)
{
U8 SFRPAGE_save = SFRPAGE;
SFRPAGE = CONFIG_PAGE;
OSCICN = 0x84; // Configure internal oscillator for
// 24 MHz / 8
SFRPAGE = ACTIVE_PAGE;
RSTSRC = 0x04; // Enable missing clock detector
SFRPAGE = SFRPAGE_save;
}
//-----------------------------------------------------------------------------
// PCA_Init
//-----------------------------------------------------------------------------
// Return Value : None
// Parameters : None
//
// This routine initializes the PCA to use the SYSCLK / 12
// as its clock source. It also sets the offset value by writing to PCA0CPL2.
//-----------------------------------------------------------------------------
void PCA_Init()
{
U8 SFRPAGE_save = SFRPAGE;
SFRPAGE = ACTIVE_PAGE;
PCA0CN = 0x40; // PCA counter enable
PCA0MD &= ~0x40 ; // Watchdog timer disabled
PCA0MD &= 0xF1; // Timebase selected - System clock / 12
PCA0CPL5 = 0xFF; // Offset value
SFRPAGE = SFRPAGE_save;
}
//-----------------------------------------------------------------------------
// PORT_Init
//-----------------------------------------------------------------------------
// Return Value : None
// Parameters : None
//
// This function configures the Crossbar and GPIO ports.
//
// P1.3 digital push-pull LED
// P1.4 digital open-drain SW1
//-----------------------------------------------------------------------------
void PORT_Init (void)
{
U8 SFRPAGE_save = SFRPAGE;
SFRPAGE = CONFIG_PAGE;
P1MDOUT |= 0x08; // Enable LED as a push-pull output
XBR2 = 0x40; // Enable crossbar and weak pull-ups
SFRPAGE = SFRPAGE_save;
}
//-----------------------------------------------------------------------------
// TIMER2_Init
//-----------------------------------------------------------------------------
// Return Value : None
// Parameters :
// 1) int counts - calculated Timer overflow rate
// range is positive range of integer: 0 to 32767
//
// Configure Timer2 to 16-bit auto-reload and generate an interrupt at
// interval specified by <counts> using SYSCLK/48 as its time base.
//-----------------------------------------------------------------------------
void TIMER2_Init (U16 counts)
{
U8 SFRPAGE_save = SFRPAGE;
SFRPAGE = ACTIVE_PAGE;
TMR2CN = 0x00; // Stop Timer2; Clear TF2;
// use SYSCLK/12 as timebase
CKCON &= ~0x60; // Timer2 clocked based on T2XCLK;
TMR2RL = -counts; // Init reload values
TMR2 = 0xFFFF; // Set to reload immediately
ET2 = 1; // Enable Timer2 interrupts
TR2 = 1; // Start Timer2
SFRPAGE = SFRPAGE_save;
}
//-----------------------------------------------------------------------------
// Interrupt Service Routines
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
// Timer2_ISR
//-----------------------------------------------------------------------------
//
// This routine changes the state of the LED whenever Timer2 overflows.
//-----------------------------------------------------------------------------
INTERRUPT (TIMER2_ISR, INTERRUPT_TIMER2)
{
TF2H = 0; // Clear Timer2 interrupt flag
LED = !LED; // Change state of LED
}
//-----------------------------------------------------------------------------
// End Of File
//-----------------------------------------------
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