Freescale MC9S12 series ATD driver

Today, I will show you the MC9S12XS128 A/D module and the development of related drivers.

What is an Analog-to-Digital (A/D) Converter

A device that can convert analog quantities into digital quantities is called an analog-to-digital (A/D) converter.

Overview of the ATD module built into the MC9S12XS

The ATD (also known as A/D) module built into the MC9S12XS128 is a 16-channel, 12-bit precision, multi-input multiplexing, successive approximation analog-to-digital converter.

Let's take a look at the basic features of the ATD module.

The ATD module has the following basic features:

l8-bit/10-bit/12-bit optional conversion accuracy;

l Conversion in stop mode uses the internal clock;

l After the conversion is completed, it will be in low power consumption state;

l Automatic and programmable value comparison, interrupt application can be set when it is greater than or less than or equal to the set value;

l Programmable sampling time;

l Left-align/right-align conversion value;

l External trigger function;

l Conversion completion interrupt request;

l 16-way analog input channel multiplexer;

l Can realize special conversion of V RH , V RL and (V RH+V RL)/2;

l The conversion sequence length is 1 to 16;

l Continuous conversion mode;

l Multi-channel scanning function;

l The external trigger function can be configured as an AD channel or 4 external additional trigger input terminals. The external trigger source can be selected as an off-chip or on-chip signal.

The MC9S12X128 ATD module registers are as follows:

I will not go into detail about the functions of each register. You can refer to the datasheet.

Let's take a look at how the AD module is implemented in detail by combining the code.

I won't talk about PLL multiplication. 

The ATD initialization module mainly includes: enabling the module, setting the conversion accuracy (currently 8-bit accuracy), conversion mode setting, clock frequency setting, etc.

To obtain the AD value of the current pin, the conversion completion flag is judged. After it is set, the corresponding register is read to obtain the current AD value.