MSP Ultra-Low Power | High Integration | Easy-to-Use “How To” Series: Clock System

Agenda  Purpose –Provide a brief but informative technical overview in “HOW-TO” use the MSP430 clock system  Objectives –Clock system basics & ULP –Clocking & MSP430 generations –Design considerations

Why is the clock system important?  The clock system is fundamental to enabling the ULP feature set of the MSP430  Careabouts:  CPU Clock –High frequency –Low power –Stable & Flexible –Fast wake-up  Peripheral Clock –High frequency –Low power –Stable & Flexible –Fast wake-up –Independent from CPU  Standby Clock –Ultra-low power –Low frequency –Accurate (RTC) –Reliable (WDT) MSP430 Ultra-Low Power Ultra-Low Power Active Mode Up to 7 Low Power Modes (LPMx) Instant Wakeup Autonomous peripheral operation in low power modes

MSP430 Clock System Basics  All ULP MSP430 devices have a fundamental clocking architecture –On-chip, high frequency, instant-on oscillator (DCO) –ULP, low frequency, kHz crystal oscillator (LFXT1)  Enables ULP embedded operation DCO for fast, low power active CPU processing LFXT1 Ultra-low power standby clock for timer wakeup DCO Instant-on ablity to service interrupts ~250uA ~1uA Always-on On demand

Breaking down the terminology  LFXT1 –This is the ULP low frequency crystal oscillator in every MSP430 device –Typical usage is with a kHz watch crystal for RTC –In some devices (2xx, 5xx, 6xx) it is also possible to source a digital clock directly to the LFXT1 input –Most devices also support a high frequency mode (see XT1) that can interface with MHz-range crystals & resonator  VLO –Extremely ULP on-chip oscillator, fixed to ~10kHz –Useful for standby clocking where power is more critical than accuracy  REFO –On-chip ULP kHz oscillator for crystal-less operation at more accurate frequencies that via the VLO  DCO –Digitally Controlled Oscillator built into every MSP430 device –Capable of 100’s kHz to 10’s MHz & is user programmable  FLL –Feature in some devices (4xx, 5xx, 6xx) that will automatically adjust the DCO frequency based on a provided reference clock  MODOSC –5MHz on-chip oscillator for automatic use with select peripherals  XT1 & XT2 –Oscillator circuit for crystals & resonators –(HF)XT1 on almost all MSP430s (except the F20xx and some G2xx devices –XT2 present only on larger pin count MSP430s (64+) –High frequency support only

Clocking & MSP430 generations Clock/ Feature Frequency Range Relative Precision Application/Devices Supported High-Frequency DCO 100kHz to 25MHz+ Low (2xx: Medium) ALL MSP430s: High frequency source for CPU & peripherals 2xx only: Integrates a high stability DCO over temp & Vcc w/ calibrated constants stored in flash for common freqs +ROSCBetter 1xx, some 2xx: Can help stabilize DCO drift over temperature using external precision resistor +FLLBest 4xx,5xx,6xx: Auto-tunes DCO based on reference clock such as 32kHz xtal HFXT1/ XT2 100’s kHz to 10’s MHz High Most MSP430s: use when high accuracy/frequency is required. Higher current than DCO. Typically, smaller devices do not support XT2 ’20xx & some G2xx devices do not support HF mode at all MODOSC5MHzMedium 5xx, 6xx: Integrate osc for auto-on use with FLASH, ADC & other modules Low-Frequency LFXT132kHzHighALL MSP430s: standard use in LPM3/3.5 & RTC applications VLO~10kHzLow 2xx, 5xx, 6xx: Integrated low freq osc consuming lowest current of any clock option REFO32kHz Medium/ High 5xx, 6xx: Integrated 32kHz osc for crystal-less applications providing reasonable accuracy

Design considerations  MSP430 has 3 clock trees –ACLK: typical use as low frequency, low power LPMx peripheral clock –MCLK: active CPU clock –SMCLK: high or low frequency peripheral clock  Design for robust 32kHz crystal operation if needed –As with any ULP oscillator, proper crystal selection, loading & PCB layout are key factors in achieving a reliable 32KHz XTAL design –Check oscillation allowance BEFORE production to address any weakness  Know the differences in device family features –Basics are the same, however a lot of variation in feature set exists –Understanding what is possible is key to realizing ULP operation  Understand device/family-specific behavior: –Active WDT: sourced from the DCO at power up/reset: handle the WDT first in your software! –Clock failsafe: crystal fault detection means safe & reliable operation but may result in incorrect frequencies. Take care to configure clocks and properly handle osc fault conditions. –Clock requests: some clocks may or may not automatically remain active when entering LPMx modes, resulting in unexpected halting of peripherals or higher than expected LPMx current consumption

References  MSP430F5xx and MSP430F6xx Core Libraries MSP430F5xx and MSP430F6xx Core Libraries –Provides functions that implement the most common operations using the PMM, UCS, PMAP and Flash modules, such as changing the core voltage to operate at higher frequencies, crystal/clock initialization, mapping port I/O, and write/erase flash operations.  MSP kHz Crystal Oscillators MSP kHz Crystal Oscillators –Describes selection of the right crystal, correct load circuit, and proper board layout key to stable crystal oscillator performance. Information regarding recommended PCB desing and possible oscillator tests to ensure stable oscillator operation in mass production are included.  MSP430 LFXT1 Oscillator Accuracy MSP430 LFXT1 Oscillator Accuracy –Details the factors that influence achievable accuracy of the low frequency oscillator, specifically for real-time clock (RTC) applications in 1xx & 4xx devices.  Microcrystal Recommendations for kHz crystals Microcrystal Recommendations  Epson Toyocom Recommendations for kHz crystals Epson Toyocom Recommendations  Your specific MSP430 device’s datasheet & Family User’s Guide

Thank you!