FLL+ Clock Module Operation
5-8
FLL+ Clock Module
5.2.3
XT2 Oscillator
Some devices have a second crystal oscillator, XT2. XT2 sources XT2CLK
and its characteristics are identical to LFXT1 in HF mode, except XT2 does not
have internal load capacitors. The required load capacitance for the high
frequency crystal or resonator must be provided externally.
The XT2OFF bit disables the XT2 oscillator if XT2CLK is unused for MCLK
(SELMx
≠
2 or CPUOFF = 1) and SMCLK (SELS = 0 or SMCLKOFF = 1).
XT2 may be used with external clock signals on the XT2IN pin. When used with
an external signal, the external frequency must meet the datasheet
parameters for XT2.
If there is only one crystal in the system it should be connected to LFXT1. Using
XT2 only will cause the LFOF fault flag to remain set not allowing for the OFIFG
to ever be cleared.
XT2 Oscillator in MSP430x47x Devices
The MSP430x47x devices have a second crystal oscillator XT2, that supports
crystals with up to 16MHz. XT2 sources XT2CLK. The XT2Sx bits select the
range of operation of XT2. The XT2OFF bit disables the XT2 oscillator if
XT2CLK is not used for MCLK or SMCLK as described above.
XT2 may be used with external clock signals on the XT2IN pin when
XT2Sx = 11. When used with an external signal, the external frequency must
meet the datasheet parameters for XT2. When the input frequency is below
the specified lower limit, the XT2OF bit may be set preventing the CPU from
being clocked with XT2CLK.
If there is only one crystal with a frequency below 8 MHz in the system, it should
be connected to LFXT1. Using XT2 only causes the LFOF fault flag to remain
set, not allowing for the OFIFG to ever be cleared.
Summary of Contents for MSP430x4xx Family
Page 1: ...MSP430x4xx Family 2007 Mixed Signal Products User s Guide SLAU056G ...
Page 2: ......
Page 6: ...vi ...
Page 114: ...3 76 RISC 16 Bit CPU ...
Page 304: ...5 20 FLL Clock Module ...
Page 340: ...7 8 Supply Voltage Supervisor ...
Page 348: ...8 8 16 Bit Hardware Multiplier ...
Page 372: ...9 24 32 Bit Hardware Multiplier ...
Page 400: ...10 28 DMA Controller ...
Page 428: ...13 10 Basic Timer1 ...
Page 466: ...15 24 Timer_A ...
Page 522: ...17 30 USART Peripheral Interface UART Mode ...
Page 544: ...18 22 USART Peripheral Interface SPI Mode ...
Page 672: ...23 12 Comparator_A ...
Page 692: ...24 20 LCD Controller ...
Page 746: ...26 28 ADC12 ...