Skip to content Skip to navigation Skip to collection information

OpenStax-CNX

You are here: Home » Content » Introduction to the Texas Instruments ez430 » 4.2 - Timers

Navigation

Lenses

What is a lens?

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

This content is ...

Affiliated with (What does "Affiliated with" mean?)

This content is either by members of the organizations listed or about topics related to the organizations listed. Click each link to see a list of all content affiliated with the organization.
  • TI MSP430 display tagshide tags

    This collection is included inLens: Texas Instruments MSP430
    By: Texas Instruments

    Comments:

    "This is the entire course organized at Rice University for all the basic lessons for using an MSP430. It is designed for the use of an eZ430 tool and is still under construction."

    Click the "TI MSP430" link to see all content affiliated with them.

    Click the tag icon tag icon to display tags associated with this content.

Recently Viewed

This feature requires Javascript to be enabled.

Tags

(What is a tag?)

These tags come from the endorsement, affiliation, and other lenses that include this content.
 

4.2 - Timers

Module by: Naren Anand. E-mail the author

Based on: Timers on the MSP430 by adrian valenzuela, CJ Ganier

Summary: The Timer A system on the ez430 is a versatile means to measure time intervals.

The Timer systems on the ez430 are a versatile means to measure time intervals. The timer (called Timer A) can measure the timing on incoming signals or control the timing on outgoing signals. This function is necessary to meet arbitrary timing requirements from outside components, and the ability is useful in phase locking scenarios etc. The Timer system is one system (and the most common system) to make use of interrupts Interrupts and Timers are bing introduced in tandem to illustrate this operation although they are seperate entities.

The most basic operation of the timer systems is that the counter in the module increments for each clock cycle. The timer clocks can be sourced from any of the clock lines discussed in Lab 3. The incoming source can be divided down by multiples of two before entering the counter. The user’s guide for the MSP has good diagrams on the architecture of the system in the respective sections for the timer. Below the features and uses of Timer A are outlined.

Timer A Modes

Timer A is a flexible system; the main counter can vary its counting pattern among several options with the MCx bits of the Timer A Control Register TACTL. These modes are:

  1. Stop: the counter is not running
  2. Up: the counter counts upward from zero to the value in Timer A Compare Latch 0 (TACL0). When it gets to this value, it resets to zero. If the TACL0 value is larger than the maximum value of the Timer A counter, the counter behaves as if it were in Continuous mode.
  3. Continuous: the counter counts from zero to the maximum value of the Timer (0xFFFF). When the counter reaches this value, it resets to zero.
  4. Up/down mode: the counter counts up to the value in TACL0 then counts back down to zero (as opposed to resetting directly to zero). If the TACL0 value is larger than the maximum value of the Timer A counter, the counter behaves as if it were in Continuous mode.

Please note that the word count is used above- if the timer is set to a certain number it will not trigger anything. The timer must count from the number below to the target number to trigger effects.

Timer A Capture Compare Register 0

There are 2 capture compare registers in Timer A. While there is only one counter for both modules, they can each interpret the count independently. The most important module is module 0 because it controls the timer with its TACL0 register. Primarily it controls rollovers, but it also has its own dedicated interrupt. Setting this module up correctly is essential for desired operation of Timer A.

What is Capture/Compare?

A capture is a record of the timer count when a specific event occurs. The capture modules of the timers are tied to external pins of the ez430. When the control registers of Timer A and the specific capture compare module have been properly configured, then the capture will record the count in the timer when the pin in question makes a specific transition (either from low to high or any transition). This capturing event can be used to trigger an interrupt so that the data can be processed before the next event. In combination with the rollover interrupt on Capture module 0, you can measure intervals longer than 1 cycle.

A compare operation is less intuitive than the capture, but it is basically the inverse of a capture. While capture mode is used to measure the time of an incoming pulse width modulation signal (a signal whose information is encoded by the time variation between signal edges), compare mode is used to generate a pulse width modulation (PWM) signal. When the timer reaches the value in a compare register, the module will give an interrupt and change the state of an output according to the other mode bits. By updating the compare register numbers, you change the timing of the signal level transitions.

This may sound somewhat complicated, but the basic concept of measuring (input) or controlling (output) the time interval between high to low and low to high transitions is all you need to know to start with. The MSP capture/compare modules have many different ways to perform each operation. This can be somewhat overwhelming, but it allows the microprocessor to handle inputs from a greater variety of other components. Capturing and comparing are done with the same modules, and each one can be configured individually. They can also be grouped using the TACTL to trigger the capture compare registers to load simultaneously (useful for compare mode). The ez430 User’s Guide fully details the behavior of the modules and the registers that control them.

Timer Interrupts

There are two interrupts related to timer A. One interrupt is dedicated to capture compare module 0; and, depending on configuration, it fires when the counter rolls back to zero. The second interrupt handles all of the modules except for the first one, and fires to indicate that the module has captured or compared as explained above. Here this simply means the interrupt handles the second module. However, in other devices that have more capture/control registers, this interrupt would handle this entire set of modules. Each module can be individually masked or enabled, and a special register stores which module caused the interrupt. As with all maskable interrupts, setting the general interrupt enable is necessary to receive them. The interrupts are important in being able to perform complex operations as new data arrives.

Collection Navigation

Content actions

Download:

Collection as:

PDF | EPUB (?)

What is an EPUB file?

EPUB is an electronic book format that can be read on a variety of mobile devices.

Downloading to a reading device

For detailed instructions on how to download this content's EPUB to your specific device, click the "(?)" link.

| More downloads ...

Module as:

PDF | More downloads ...

Add:

Collection to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks

Module to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks