Why use a microcontroller?

AN414

4/14

Doc ID 1876 Rev 2

ST6265C MCU approach, the MCU itself can sense the buttons, potentiometers, drive

LEDS...

In some existing appliances, the analog approach is used in conjunction with a

microcontroller, the latter being dedicated to the user interface. This is obviously a

waste, as one ST62 MCU could take care of both tasks. If we consider the case of LCD

displays, which are becoming more and more popular, a dedicated LCD driver circuit is

generally used to interface them to a micro.

We have implemented a software LCD drive function in the ST6265C MCU, using its

free output pins; the ST6265C MCU can at the same time run the motor, drive the LCD

and sense the user speed demand (in our case, two buttons "faster" and "slower"). (Cf.

ref. [4] page 12).

2.

Time-to-market and design time must be considered: the ST6265C MCU software

contains all the characteristics of the application; it is much faster, if the application

must be modified, to modify software than hardware especially when OTP parts are

used for volume production.

We have implemented a software motor power limitation: the motor characteristics are

known by the software in the form of a look up table. If the application must

accommodate a different motor type, it is very quick to modify the data table in the

software. Most modifications of the application can be achieved by simple software

modifications.

If the ST6265C MCU replaces an ASIC, the time and money saved when it is

necessary to modify the initial design goes without saying. The ST62 MCU can also be

used to customize the application: to limit the stock inventory, several applications, for

example a low-end and high-end vacuum cleaner can use the same electronics board,

with the same MCU, but the MCUs have different softwares, or the software is

programmed into the ST62T65Cxx order codes (OTP version of ST6265C) at the end

of the board assembly line.

3.

The MCU lets you do things that are not possible otherwise. Simple examples are:

a)

Execute pre-programmed sequences of motor speeds, diagnostic faults and alert

the user (with temperature sensors, speed sensors, ... or sometimes without them,

by deducing motor speed from current, or temperature from cumulated current ...).

b)

Store in non-volatile memory (EEPROM) user settings which must be saved when

power is turned off.