A digit-to-analog converter (DAC) is a device that converts a digital signal into an analog signal in electronics.
The DAC APIs provide a set of methods for DAC data transfer, including:
- Opening or closing a DAC device
- Setting the target digital-to-analog (DA) value
### Basic Concepts
The DAC module provides the output channel for the process control computer system. It connects to the executor to implement automatic control of the production process. It is also an important module in the analog-to-digital converter using feedback technologies.
- Resolution
The number of binary bits that can be converted by a DAC. A greater number of bits indicates a higher resolution.
- Conversion precision
Difference between the actual output value of the DAC and the theoretical value when the maximum value is added to the input end. The conversion precision of a DAC converter varies depending on the structure of the chip integrated on the DAC and the interface circuit configuration. The ideal conversion precision value should be as small as possible. To achieve optimal DAC conversion precision, the DAC must have high resolution. In addition, errors in the devices or power supply of the interface circuits will affect the conversion precision. When the error exceeds a certain degree, a DAC conversion error will be caused.
- Conversion speed
The conversion speed is determined by the setup time. The setup time is the period from the time the input suddenly changes from all 0s to all 1s to the time the output voltage remains within the FSR ± ½LSB (or FSR ± x%FSR). It is the maximum response time of the DAC, and hence used to measure the conversion speed.
The full scale range (FSR) is the maximum range of the output signal amplitude of a DAC. Different DACs have different FSRs, which can be limited by positive and negative currents or voltages.
The least significant byte (LSB) refers to bit 0 (the least significant bit) in a binary number.
### Working Principles
In the Hardware Driver Foundation (HDF), the DAC module uses the unified service mode for API adaptation. In this mode, a device service is used as the DAC manager to handle access requests from the devices of the same type in a unified manner. The unified service mode applies to the scenario where there are many device objects of the same type. If the independent service mode is used, more device nodes need to be configured and memory resources will be consumed by services. The figure below shows the unified service mode.
The DAC module is divided into the following layers:
- The interface layer provides APIs for opening or closing a device and writing data.
- The core layer provides the capabilities of binding, initializing, and releasing devices.
- The adaptation layer implements other functions.
NOTE<br/>The core layer can call the functions of the interface layer and uses the hook to call functions of the adaptation layer. In this way, the adaptation layer can indirectly call the functions of the interface layer, but the interface layer cannot call the functions of the adaptation layer.
**Figure 1** Unified service mode
![Unified service mode](figures/Unified_service_mode.png"DAC unified service mode")
### Constraints
Currently, the DAC module supports only the kernels (LiteOS) of mini and small systems.
## Development Guidelines
### When to Use
The DAC module converts digital signals into analog signals in the form of current, voltage, or charge. It is mainly used in audio devices. Audio players and headsets use the DAC module as the digital-to-analog conversion channels.
### Available APIs
The table below describes the APIs of the DAC module. For more details, see API Reference.
