Using MSP430 with alternate Crystal oscillator

If you need accuracy than only you need crystal. Otherwise we have a very wide range of internal freq ie from 1.5 KHz to 16 MHz

Connecting External ckt also depends on there accuracy like capacitor but inbuilt are more accurate.

I think you should use internal capacitance.

Tim,

An external TCXO is always going to give you the best accuracy, especially if you can use it directly for you MCLK (and not use the internal DCO/FLL function, which adds jitter).

You do not mention which part you are using. Some only support low-frequency crystals on XT1, some support high-frequency on XT1 (HF mode) and some have a HF XT2 input.

Look in the datasheets for the parts you are considering to determine what options are available to you. But short answer is Yes, if you choose the correct MSP430 device.

I am considering using the MSP430 Launchpad device.  http://www.ti.com/tool/msp-exp430g2#supportandcommunity

The Crystal Oscillator I am considering is 12 MHz, which should fit it seems on either the XT1 or the XT2.

How can you compare an external oscillator (12 MHz) with an internal oscillator(XT2).

External may be accurate but internal is processed and refined than external may not.

Tim Wright said:

which should fit it seems on either the XT1 or the XT2.

What XT2? The G series (LaunchPad) processors only have XT1. Using a 12MHz oscillator has been tested about a yearo ago and worked. However, keep in mind that this is outide the official specs, so  new devices or device revisions might fail to support it.

vikas dabas said:

How can you compare an external oscillator (12 MHz) with an internal oscillator(XT2).

External may be accurate but internal is processed and refined than external may not.

On the 550x/5510 devices, at least, the internal oscillator has a full temperature range of 3.5% (page 55 of SLAS645G). That is 35,000 parts-per-million.

Compare that to an external crystal and/or oscillator typically 100 ppm.

The internal oscillator is 350 times WORSE when it comes to frequency tolerance.

The user guide referred me to the MSP430x2xx Family User's Guide for more information, and on there it talked about connecting external oscillators.  I assumed this meant that any MSP 430 with F2 or G2 could have that capability.

P.S. thank you for your help, I am an engineering student working on making a clock with this chip and this conversation has been lots of help for me.

Brian Boorman said:

On the 550x/5510 devices, at least, the internal oscillator has a full temperature range of 3.5%

He said "internal oscillator (XT2)" which implies he's talkign about the XT2 oscillator with external crystal, in opposition to an external oscillator that produces a TTL clock signal.
Of course the itnernal XT2 oscillator circuit has no tolerance at all. It completely depends on the crystal precision. And the attached load capacitance (whcih affects crystal precision).

Of course the internal DCO has a rather large temperature range and worse tolerance. But that wasn't the topic.

Tim Wright said:

on there it talked about connecting external oscillators.  I assumed this meant that any MSP 430 with F2 or G2 could have that capability.

It has, by setting XT1 (there is no XT2) in bypass mode. And as I said, depite the fact that the datasheet only specifies 50kHz even in bypass mode with external Oscillator, devices under test have accepted high-speed clock signals too.

But I guess, the additional price for the oscillator, compared to a mere crystal, makes up for the lowered price of the G series devices. Unless you already have a TTL clock signal on your PCB anyway.

I may be wrong, but the fact (unless I missed a device) that there i sno DIP device with HF crystal capability, might indicate that the DIP package isn't suited for HF crystal operation. Maybe due to the additional pin capacitance, crosstalk, whatever. But this may be plain coincidence too.

Jens-Michael Gross said:

It completely depends on the crystal precision. And the attached load capacitance (whcih affects crystal precision).

The following report illustrates this, but it's a bit older and makes observations concerning the LFXT1 and not the XT2. It provides an understanding of some factors influencing achievable accuracy. It can be used as additional information for those interested.

MSP430 LFXT1 Oscillator Accuracy

Christian Steffen said:

The following report illustrates this,

Thanks for providing the link. The LFXT1 oscillator and the HFXT1/XT2 oscillator are a little bit different. I guess, the series capacitance tfor current reduction isn't there in HF mode. Also, the gate capacitances in fF range are even less important sicne HF crystals usually have a higher load capacitance.
But in general, it covers the topic nicely.