Tinkering TI MSP430F5529

Timer Overview

MSP430F5529 microcontroller has six timers divided in three categories – General Purpose Timers like Timer A and Timer B, Watchdog Timer (WDT) and Real Time Clock (RTC).

There are

  • 3 Timer As – T0A5, T1A3 and T2A3
  • 1 Timer B – T0B7
  • 1 WDT_A
  • 1 RTC_A

The cut-away block diagram of MSP430F5529’s internal peripherals shown below highlights these timers.

Timer A and Timer B are almost same with minor differences. Timer B offers better PWM options. As their names suggest, RTC_A and WDTA_A are specialized timers for specific or special purposes. They can be alternatively used like regular timers with some limitations.

These timers can be fed with bewildering number of clock combinations offered by the UCS. There are options for external sources in some cases too. The structures and the operations of all of these timers is similar to what we have seen in my previous MSP430 tutorial. The only exception is the RTC_A module as this timer was not available then. Before trying to use any timer, it is my recommendation to go through the driverlib files of the respective timer. This will enable visualizing what can and cannot be done with a given timer module. This also reduces time to read technical documents and datasheet. However, I will still recommend reading these docs should one want to master the timers.

Timer A and B are 16-bit general-purpose timers with capture-compare (CC) modules. The CC modules can be used for either capturing waveforms or PWM/waveform generations. If CC modules are not needed, these timers can be used for timing events and keeping track of time.  In TI’s literature, we will see that timers are named as TxYn where Y represents timer class/category, i.e. Timer A, Timer B, etc, x represents timer number or instantiation and n represents number of CC channels. Therefore, T0A5 means 0th instantiation of Timer A having 5 CC channels or simply 0th A-type timer having 5 CC channels. Sometimes, the CC channels are ignored and the timers are simply named like TA2. This naming states 2nd instantiation of Timer A or simply 2nd A-type Timer. Thus, there is a short naming format and a long naming format for general purpose timers.

MSP430x5xxx and MSP430x6xxx family of microcontrollers have three types of RTCs and they vary slightly in some features. MSP430F5529 has one RTC_A module which is the basic of all three types. RTC_A lacks battery-backup option unlike other RTCs. RTC_A is a special timer with a 32-bit counter that is intended for time-keeping applications, i.e., clock and calendar. Since time-keeping needs to be very accurate, RTC has special hardware arrangements to take care of so. It is my personal recommendation to use dedicated 32.768 kHz temperature-compensated crystal oscillator (TCXO) as the source of RTC_A clock. This will ensure better accuracy and precision. It is a common problem for most RTCs to either lead ahead or lack behind actual time. RTC_A can also be used as a 32-bit timer if time-keeping is not needed. However, there are no hardware CC channels with RTC_A.

WDT_A is similar but more advanced than the WDT+ seen in my previous MSP430 tutorial. It has 8 timer intervals rather than 4. This special timer is primarily intended for avoiding erratic/irresponsive behaviour in the event of an electromagnetic interference (EMI) or conditions that leave a micro into an unforeseen loop or other software issue. Again, this timer can be alternatively used like a regular timer if watchdog feature is not needed. However, this timer too doesn’t have any CC channel.

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