a round up of microcontroller interfacing techniques

Micro-controllers are useful to the extent that they communicate with other devices, such as sensors, motors, switches, keypads, displays, memory and even other micro-controllers.Many interface methods have been developed over the years to solve the complex problem of balancing circuit design criteria such as features, cost, size, weight, power consumption,reliability, availability, manufacturability.

The following document is a summary of some of these interfacing techniques
http://www.bipom.com/applications/micro_interfacing.pdf