Keeping Time on MSP430

kpbr

Other Parts Discussed in Thread: MSP430F1232

My application requires that I keep track of time between events. I detect the events from reading an external signal with the ADC10 and an algorithm.

I'd like to keep track of time accurate up to 10ths of a second, possible 100ths if needed.

Right now I've got timer A interrupting roughly 10 times a second. I increment a variable each time this occurs and reset it when I detect an event has occurred. While I feel this does an OK job, I feel I should make it more accurate due to drift in the timer interrupt with temperature change, etc.

Is there a way I can do this with software? It is my understanding that many people will solder on an external watch crystal, but I'm wondering if there are other things I could explore.

Thanks!

over 16 years ago

0 BrandonAzbell over 16 years ago

TI__Guru 64600 points

The use of an external watch crystal allows you to get a true time base within the bounds of temperature drift, etc. This is often used when needing to create a Real Time Clock scenario with the Low Frequency Oscillator on the MSP430.

It is possible to use just the DCO on the MSP430 and a timer to implement a timebase, but it will not be accurate from the perspective of keeping time, as it will have drift where you may lose some seconds over the course of the day. I have implementing a tick counter that used a MSP430 running at 8MHz (ie. MSP430F1232) which emulated a 1 millisecond count using the Timer_A for the timebase. The interrupt service routine for the Timer_A implemented the managing of the time variables I was trying to create such as millisecond, second, minute, etc.

0 KCheung over 16 years ago

Intellectual 455 points

Hi,

I'm trying to do exactly what you're doing in terms of using the software to keep track of real time. I was wondering if you could either give me some advice or some code to how you implemented this.

Thanks!

0 Joerg Quinten over 16 years ago in reply to KCheung

Guru 17650 points

Hi,

if you want to have a accurate real-time-clock (RTC) use an external watch crystal and i.e. this library form TI (http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slaa290).

Rgds
aBUGSworstnightmare

0 Roger Williams over 14 years ago in reply to Joerg Quinten

Prodigy 10 points

Hello,

Complete MSP430 newbie here.

I have the Launchpad and am getting my feet wet by trying to set up an actual 4 digit clock.

I have read two AP's one of which is SLAA290. However, I cannot find the zip file. I have tried searches and have come across people saying they have had problems with the code.

I would really like to see GRACE have a real-time clock example setup.

I would also really appreciate any bits of code to help me along understanding the setup and interrupt handling.

As far as display digits, I can worry about that later.

Thanks!

0 Joerg Quinten over 14 years ago in reply to Roger Williams

Guru 17650 points

Hi Roger,

have a look at the LaunchPad wiki (http://processors.wiki.ti.com/index.php?title=MSP430_LaunchPad_(MSP-EXP430G2)) - there you can find some links to much more resources - i.e to www.43oh.com.

And they feature here http://www.43oh.com/2010/08/an-msp430-based-clock/ what you're looking for!

Rgds
aBUGSworstnightmare

0 William Goh over 14 years ago in reply to Roger Williams

TI__Genius 16215 points

Roger,

SLAA290 zip file is located here on the web. Link.

SLAA290 document is located here on the web. Link.

Another great place for learning and understanding how tot setup the various peripherals in the msp430, you could check out our Code Example site here.

As for Grace, this is definitely a good piece of feedback moving forward on how Grace should evolve in the future. As of now, Grace is designed specifically to only initialize peripherals.

Regards,

William

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Keeping Time on MSP430