There are many different forms of micro-controller and a manufacturer, selecting the proper micro-controller for your application is one of the critical decisions which controls the success or failure of your project. The main goal is to select the least expensive micro-controller while still fulfilling the system specification i.e. performance, reliability, environmental etc. The cost should also include the Engineering Research and development (R&D), manufacturing, warranty repairs, updates, field service and upward compatibility and finally ease of use amongst many other factors. The major selection criteria are the balance between data processing and control requirements. Simple micro-controller allow a limited set of instructions with a large number of I/O pins , while those with advanced instructions i.e. Sin, Cos maths functions  have more 'data processing' skills and a reduced amount of I/O pins. In order to help below is shown a few selection criteria questions

1)  Can the micro-controller do the job?

a)   Does it have the required number of I/O pins/port i.e. if too many extra cost.

b)  Do you require any other peripherals such as serial I/O , Ram , ROM , A/D , D/A etc.

c)  Does it have other peripherals which are not needed?

d)  Does the CPU core have the correct throughput i.e. computing power to handle the system requirements or choice of language HLL or LLL , too much waste , too little never work

e)   Is the controller affordable?

f)  Is the memory size big enough for the software?