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lecNew-10-Timer - WPI ECE2801 Foundations of Embedded...

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WPI ECE2801 Foundations of Embedded Computer Systems Lecture 10: Timers and Interrupts
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EE2801: Foundations of Embedded Systems Lecture 10 Review: System Clocks Clock sources LFXT1CLK = LF Crystal 32,768 Hz watch crystal XT2CLK = 8MHz crystal DCOCLK = Internal Digitally Controlled Oscillator (frequency selectable) 4 clock signals to CPU and peripherals (DEFAULTS on Reset to the following. ..) MCLK = Master Clock (CPU) = 32*LFXT1CLK = 1.048567 MHz SMCLK = Submain Clock = DCOCLK = 1.048567 MHz ACLK = Auxiliary Clock = LFXT1CLK = 32,768 Hz ACLK/n = Buffered Clock Output; n = 1,2,4,8 Clock sources/speeds for CPU and peripherals are software selectable, controlled through FLL+ Clock Module Registers (see User Guide Chapter 4.)
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EE2801: Foundations of Embedded Systems Lecture 9 Timers Timers: digital circuit block that counts clock ticks Can operate in a number of common modes Up (or Down) mode Continuous Mode Up/Down mode Timers can be polled (count register) or generate interrupts
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EE2801: Foundations of Embedded Systems Lecture 10 The MSP430F449 Timers Watchdog Timer (WDT) The Watchdog timer is a 16-bit timer. Its primary function is to perform a controlled system restart after a software problem occurs. A system reset is generated if the watchdog timer expires. The WDT module is automatically configured in the watchdog mode with an initial 32ms reset interval. The program needs to “pet the dog” to avoid system reset. WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer If this function is not needed, the watchdog function can be disabled and the module be configured as an internal timer. Basic Timer1 The Basic Timer1 module is two independent 8-bit timers. It supplies LCD timing and low frequency time intervals. It is capable of generating interrupts. The two 8-bit times can be cascaded to for one 16-bit timer. See User’s Guide Chapter 11. (used by LCD display in our development board)
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This note was uploaded on 10/12/2009 for the course ECE 2801 taught by Professor Jarvis during the Spring '08 term at WPI.

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lecNew-10-Timer - WPI ECE2801 Foundations of Embedded...

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