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MSP430 Ultra-Low Power 16-bit Microcontroller Forum
problem about LFXT1 of msp430f169
I have some question about LFXT1 of msp430f169:(1)Can a crystal of 100kHz be used in LF mode?Because I want a 10us time piece in LPM3. In fact I have used a crystal of 100kHz on my application, and I haven't found any problem.Is there any problem if I use a 100kHz crystal? (2)In msp430x1xx user guide It is mentioned that "Internal 12-pF load capacitors are provided for LFXT1 in LF mode. The capacitors add serially,providing a match for standard 32,768-Hz crystals requiring a 6-pF load." But crystal recommendation of MicroCrystal for MSP430x1xx is 9pF or 12.5pF. Can I use a 12.5pF crystal in LF mode without any other additional capacitors?(3)In datasheet of msp430f169 it it mentioned that "A 5.1MΩ resistor from XOUT to VSS is recommended when VCC <2.5 V". The function of the resistor is what? In my application supply voltage of msp430f169 is 2V - 3V,and I didn't add the 5.1MΩ resistor. Is there any problem? How should I do?
Can a 5.1MΩ resistor be added when VCC>2.5V?
thank you very much.
The 169 has exactly 12pF chip capacitance in LF mode and 2pF (parasitic pin capacitance) in HF mode. This gives you a load of 6pF in LF mode and 1pF in HF mode
in LF mode, the oscillator is optimized for 32768Hz crystals. A 100kHz crystal is far outside the specs.
In HF mode, the oscillator is designed for resonators above 450kHz and crystals above 1MHz. I suggest using an 800kHz resonator (or try a crystal wiht 800kHz, it might work) and use the DIVA_3 setting for 100kHz ACLK. External capacitors are required.
XT2 input does not have an LF mode. XT2 can only be used for clockign SMCLK and MCLK, not for ACLK. XT1 can only be used for MCLK and ACLK, not for SMCLK.
Later MSP families have a wider operating range for LF and HF mode of XT1 and allow more combinations in distributing oscillators to clocks. But the 1x family is the oldest and most restricted.
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thank you, Jens-Michael
Like you said, In HF mode, use an 800kHz crystal ,and use the DIVA_3 setting for 100kHz ACLK, in lPM3, the current consumption maybe too high for my application.
And about my third question,
In datasheet of msp430f169 it it mentioned that "A 5.1MΩ resistor from XOUT to VSS is recommended when VCC <2.5 V". The function of the resistor is what? In my application supply voltage of msp430f169is 2V - 3V,and I didn't use the 5.1MΩ resistor. Is there any problem? How should I do?
Can a 5.1MΩ resistor be used when VCC>2.5V?
bozhi main lPM3, the current consumption maybe too high for my application.
bozhi maIn datasheet of msp430f169 it it mentioned that "A 5.1MΩ resistor from XOUT to VSS is recommended when VCC <2.5 V". The function of the resistor is what?
bozhi maCan a 5.1MΩ resistor be used when VCC>2.5V?
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