There are several reasons to use a low-cost embedded microcontroller connected to the display module:
- The I/O has a real-time component that the display module is not best suited to provide. For example, A/D conversions with averaging for noise reduction, solenoid control with overload sensor that needs millisecond timing, Infra Red (IR) remote control reception.
- Flexibility is more important than cost. Using an attached micrcontroller doing device-specific I/O, it is easier to handle changes in I/O requirements and different device models with different I/O needs. In these cases, the display module stays the same, and the simpler and lower cost I/O board can be changed as needed.
- Medical or other safety requirements must be met. Having a display module do all the high level interactions (network, storage, etc.) can allow a relatively simple controller to perform the actions that are safety-related. A simple system is much easier to classify as Software of Known Provenance for regulatory reasons. There are also high reliability microcontrollers available such as TI Hercules family. If the communication with the display module is designed correctly, the display module can be classified as being of Unknown Provenance and not storing any data that relates to safe operation. In other words, it operates more like a passive display (think 7-segment numeric) just showing what it’s told.
Get more details on how the Reach display module software supports an attached microcontroller architecture.