Crystal Oscillators Using MSP430

This post is a recapture of content that previously resided on the wiki:

What are crystal specifications necessary for stable operation of a MSP430 crystal oscillator?

The main important specifications of a crystal for the MSP430 are:

• Load Capacitance(Effective Load Capacitance) : Crystal manufacturers typically define the effective load capacitance in the crystal's data sheet. Electrically, the capacitors are connected serially on pins XIN and XOUT and the effective load capacitance is then: C(eff) = {C(XIN) × C(XOUT)}/{C(XIN) + C(XOUT)} So, an effective load capacitance of 12pF specified by the crystal's data sheet requires 22pF (2 * 12pF = 24pF = 22pF + 2pF parasitic capacitance) at each pin XIN and XOUT.
• ESR (Equivalent Series Resistance) : For stable operation of an oscillator the MSP430x1xx and MSP430x3xx series both need a 32kHz crystal with an ESR < 50kOhm. The new Low-Power-Oscillator of the MSP430x4xx family and high frequency crystals for any MSP430 don't have this limitation. Up to now we rarely have seen 32kHz SMD crystals with ESR < 50kOhm.

Crystal Design considerations: 

1.  Keep the signal lines between the crystal, eventually necessary external capacitors and the MSP430 as short as possible. Very low currents are flowing in a crystal oscillator and hence long lines make it very sensitive to EMC, ESD and crosstalk. Long lines also add parasitic capacitance to the oscillator.
2. If the MSP430 is in a socket: Please be aware that the socket adds parasitic capacitance to the oscillator.
3. Keep other clock lines and often switching signal lines as far away from the crystal connections as possible.
4. Guard the crystal traces with ground traces.
5. Solder the crystal housing to GND.
6. The LFXT1 oscillator of MSP430x1xx requires in LF mode a 5.1MOhm resistor from XOUT to VSS when VCC < 2.5 V. Please have a look at the data sheet for details.

Please be aware, that in a crystal oscillator everything must fit together perfectly. Hence you have to select a crystal and external capacitors that work perfect with the internal oscillator of the MSP430.

There are many valuable PCB crystal design considerations listed in the application report SLAA322

Ancillary References

There are many valuable PCB crystal design considerations listed in the application report SLAA322

You may also be interested in the following LFXT1 accuracy report

Finally the User's Guide discusses crystal setup steps in chapter 5.