ECE 447 Fall 2009ECE 447 Fall 2009.pptVIP

ECE 447 Fall 2009 Lecture 13: TI MSP430 Watchdog Timer and Real-Time Clock ECE447: MSP430 Watchdog Timer Concept A watchdog timer (or computer operating properly timer) is a hardware timing device that triggers a system reset if the main program, due to some fault condition, such as a hang, neglects to regularly service the watchdog. ECE447: Use Cases for Watchdog Timer Out of Control Software: Trapped in infinite loop Code/Memory overwrite Peripheral Failure: Polling a non responsive device SW controlled reset: The WDT register can be used to force a reset purposely ECE 447: Enabling and Disabling the WDT The WDT is always active after a reset Default settings allow the software about 32ms to clear, stop, or reconfigure the WDT at startup. Up until now we have always stopped the WDT by setting the WDT-HOLD bit. ECE447: Petting the Watchdog Petting is performed by writing to the WDT-CNTCL bit. All writes to the WDT register are protected by a 8 bit password. 0x5A must be the upper byte value of any write to the WDTCTL register Any other value will cause an immediate reset. ECE 447: WDT Control Register ECE447: MSP430 Basic Timer1 Basic Timer 1 provides two or three fucntions in the MSP430: Clock for the LCD module Periodic Interrupts 1Hz clock signal to drive the Real-Time Clock The RTC only exists in newer MSP430xFxx family devices. ECE447: MSP430 Basic Timer1 BTCNT1 and BTCNT2 count based on control bits in BTFRQx and BTIPx. BTCNT2 causes the BTIFG flasg to be set at each rollover, with a rame from 16ms to 2s. ECE447: MSP430 Real Timer Clock Concept A Real-Time Clock (RTC) is a hardware device that counts time based on seconds, minutes, hours, days, months, and year. Unlike most clocks in a microcontroller that do not convey useful data directly, the RTC is directly human understandable. ECE447: MSP430 Real Timer Clock Concept The current time and date are held in a set of registers that contain the following bytes: Second (RTCSEC) Minute (RTCMIN) Hour (R