Digital Interface Design and Application

2 Simple Input and Output Functions

Simple input and output (I/O) operations are a fundamental part of any embedded system where an LED indicator is turned on or a user input button is provided. All processors for embedded applications provide I/O functions that can perform this kind of job and the STM32F4 ARM based processor actually includes 144 pins (16 pins on each of 9 ports) for this kind of application but as will be shown later many are associated with other functions.

2.1 Introduction

This chapter will focus on the design and application of simple I/O techniques using exclusively the basic logic elements outlined in Chapter 1, specifically latches, tri-state gates and address decoding logic. Most importantly it will develop the concept of a programme controlled interface and C language program examples, using pointers to handle interface addresses, will be described. The chapter will also cover the development of these techniques for the extensive range of reconfigurable I/O functions provided by the STM32F4, a typical embedded processor design based on the ARM core. To enable the user to handle their configuration and use conveniently, C programme techniques will be discussed. At first acquaintance, the STM32F4 embedded processor’s interface modules appear extremely complex but approaching their functionality from a simple standpoint will facilitate their effective employment in any particular application. User I/O programming in assembler will be briefly discussed ...