Data Acquisition and Control

Abstract

The input of information, such as a digital representation of a physical variable, or the output of a control signal to switch a device on or off, is accomplished through the computer ports. If the ports are ‘memory mapped‘, i.e. each port occupying one specific byte of memory, then access is achieved by using the BASIC keywords PEEK and POKE. The contents of any byte in the computer memory can be read using the PEEK command and, similarly, the contents of any address can be altered by using POKE. While PEEK is reasonably but not always harmless, POKE must be used with some care since it is possible to access areas of memory which are used by the computer’s operating system. In so doing, one might inadvertently cause the operating system to crash. If the reader is unfamiliar with memory mapped systems, then reference should be made to section 5.5 before proceeding here.