Introduction

It is very often necessary to transfer information from one piece of equipment to another, or one place to another for example printing data from a computer or monitoring remote equipment. There are many applications that use high-speed links like Ethernet, WiFi, GPRS, USB or Firewire (IEE1394) to transfer data. These systems take considerable effort and resources to implement from scratch and are best addressed by using standard off-the-shelf systems. This chapter is aimed at providing information on methods that are applicable to microcontroller-based designs where specific needs or cost rules out the use of the previously mentioned systems.

Some applications of digital circuitry make use of the digital data at the time when they are obtained. A digital voltmeter, for example, displays the obtained data as soon as the data are collected, and there is not necessarily a requirement to transfer digital data from one piece of equipment to another. In many other applications, however, and particularly in control and computing, data have to be transferred over distances that range from a metre or less up to the maximum distance that a radio signal can reach. In this chapter, we shall look at data transfer methods.

The simplest method of transferring digital data is to connect to a microprocessor bus, usually by way of buffer or transceiver chip. The transfer of data from one board to another in a digital system makes use of the microprocessor bus either directly or by way of buffer circuits, the bus