MSP430 clock selection, how to see what clock is selected in the program?

Function selection register pxsel

The function of the interface pins varies depending on the function of the peripheral module. Refer to the device's documentation to determine the function of the pins.

Each bit of the PXSEL register is selected for the function of the pin – the normal IO function or the peripheral module function.

Bit zero: The pin is selected as the normal IO function.

Bit 1: The pin is selected as the peripheral module function.

Setting pxselx = 1 does not automatically set the input and output methods of the pins. Other peripheral module functions need to be based on the function of the module.

The pxselx bit can be set in the desired direction. Refer to the pin diagram in the documentation.

Note: When pxsel=1, the interrupt function of the P1 and P2 ports is turned off.

When any bit of the PXSEL is asserted, the interrupt function of the corresponding pin is turned off. Hence introduced from these pins.

The signal cannot trigger a P1 or P2 port interrupt, regardless of the state of the corresponding P1IE and P2IE registers.

When the pin of an interface is selected as the output to the peripheral, this input to the peripheral.

The outgoing signal is the latch request signal of the pin of the device. When pxselx=1, the internal input signal.

The signal of this pin will be followed. However, if pxselx=0, go to the periphery before pxselx reset.

The input of the device will keep the input signal value of this pin unchanged.

Connect the ,, pin to the oscilloscope, look at the waveform, and it's OK!

1. The datasheet explains that when the external crystal oscillator is stopped, the microcontroller works in Low-Power Mode 4 (LPM4) mode. That is, the external crystal oscillator can be disconnected, and the machine will work in low-power mode 4. In general, a microcontroller with an internal oscillator has a low oscillator oscillation frequency and is generally not used as a clock working at full speed.

Internal oscillators are typically high-accuracy RC oscillators that are primarily used in low-power modes or to clock on-chip timing counters.

2. Correct. The frequency of the external crystal oscillator is the frequency of the ACLK.

3. Generally, single-chip microcomputers have a maximum working frequency, and single-chip microcomputers should not work in the case of greater than this frequency. If you connect an external 12m crystal oscillator, it means that the microcontroller will work at a frequency of 12m. The working frequency of the single-chip microcomputer is greater than its nominal frequency, which will make it heat up and even make some parts inside work abnormally.

So it's best not to use it in such situations, although it's possible for a microcontroller to work fine.