As we all know that HART communication chip A5191HRT needs 460.8KHz passive crystal to run, as the perfect compatible chip of A5191HRT, HT1200M also needs 460.8KHz passive crystal for the chip to use. HT1200M chip development using the clock usually have three methods, respectively, the use of external 460.8KHz passive crystal, the use of microcontroller MCO pin (MCO on behalf of the Microcontroller Clock Output, which is a microcontroller clock output pin), the use of microcontroller timer PWM output method. The following is a brief description of each.

Way 1: Use external 460.8KHz passive crystal oscillator

HT1200M clock input pin connection 460.8KHz, this method of use is also the most used over the years, the following figure is the HT1200M and passive crystal connection schematic.

Way 2: Output using the MCO of the microcontroller

The example of using a 3.6868MHz passive crystal for the microcontroller STM32L010RBT6 is illustrated.

● The HT1200M chip's pin 17 "OXTL" is connected to the microcontroller's MCO output pin (i.e., labeled ACLK), and pin 18 "IXTL" is connected to the microcontroller's "GND ".

●Open the STM32CubeMX executable program, select the STM32L010RBT6 microcontroller, and enter the following interface.

● Enter the System Core menu item and click RCC to enter the RCC Mode and Configuration interface, select Crystal/Ceramic Resonator in the Hight Speed Clock (HSE) drop-down menu, and check Master Clock Output 1.

● Click Clock Configuration interface, input 3.6864MHz in input frequency box; select HSE for System Clock Mux.

● System Clock Mux selects HSE; MCO Source Mux selects SYSCLK, and the crossover frequency box selects "/8", which can get the crossover frequency of 0.4608MHz and output it to the pin of MCO.

● Go to System Core menu item and click SYS, enter SYS Mode and Congfiguration interface, check Debug Serial Wire.

● After the configuration is completed, generate the code and run it, and capture the pin signal of MCU MCO through the oscilloscope to get the waveform (460.8KHz) as follows.

Way 3: Using the timer PWM output mode of the microcontroller

Timer output mode to the microcontroller STM32L010RBT6 using 3.6868MHz passive crystal as, signal output pin PA0 as an example to illustrate.

● The HT1200M chip's pin 17 "OXTL" is connected to the microcontroller's PA0 pin (i.e., labeled ACLK), and pin 18 "IXTL" is connected to the microcontroller's "GND ".

● Open the STM32CubeMX executable program, select the STM32L010RBT6 microcontroller, and enter the following interface.

● Open STM32CubeMX executable program, select STM32L010RBT6 microcontroller, and then enter the following interface.

● Click Clock Configuration interface, input frequency box: 3.6864MHz; System Clock Mux select HSE.

● Enter System Core menu item and click SYS, enter SYS Mode and Congfiguration interface, select Debug Serial Wire.

● Select TIM2 in Timers, select Internal Clock for Clock Source; select PWM Generation CH1 for channel1.

● Under Configuration->Parameter Settings->Counter Settings in TIM2 menu, set the variables Prescaler (PSC-16 bits value: 1; Counter Period (AutoReload Register-16 bits value): 1; Counter Period (AutoReload Register-16 bits value): 1; Counter Period (AutoReload Register-16 bits value): 1; Counter Period (AutoReload Register-16 bits value): 1. value): 1

● After the configuration is completed, generate the code, in the main( ) program, add the capture/comparison register (CCR) related code.

● Run the code in the microcontroller's PA0 pin output signal through the oscilloscope to capture the following waveform graph (460.8KHz)

The above three clock output methods, external passive crystal and MCO output methods are the most commonly used, and the timer method is the most flexible, I hope to give you some help in the development process of HART communication.

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