tailieunhanh - Interfacing PIC Microcontrollers 3

Interfacing PIC Microcontrollers 3. Explore in detail microcontroller interfacing techniques using the popular PIC 16F877 Work through step-by-step examples interactively using circuit simulation software, supplied as assembly source code Gain the knowledge of a wide range of peripheral devices such as keyboards, displays, sensors and drives and serial communication with other processors, memory and more Use interactive simulation software to design and test circuits. | Interfacing PIC Microcontrollers Thus a list of instructions in memory is executed in turn to carry out the required process. In a word processor for example keystrokes are read in via the keyboard port stored as character codes and sent to a screen output for display. In a game input from the switches on the control pad are processed and used to modify the screen. In this case speed of the system is a critical factor. Memory There are two types of memory volatile and non-volatile. Volatile memory loses its data when switched off but can be written by the CPU to store current data this is RAM Random Access Memory . ROM Read Only Memory is non-volatile and retains its data when switched off. In a PC a small ROM is used to get the system started when it is switched on it contains the BIOS Basic Input Output System program. However the main Operating System OS for example Windows and application program . Word have to be loaded into RAM from Hard Disk Drive HDD which takes some time as you may have noticed So why not put the OS in ROM where it would be instantly available Well RAM is faster cheaper and more compact and the OS can be changed or upgraded if required. In addition an OS such as Windows is very large and some elements are only loaded into RAM as needed. In addition numerous applications can be stored on disk and loaded only as required. The ideal memory is non-volatile read and write fast large and cheap. Unfortunately it does not exist Therefore we have a range of memory technologies as shown in Table which provide different advantages which ROM Flash ROM RAM CD-ROM DVD-RW HDD Description Chip Chip Chip Optical disk Optical disk Magnetic disk Sample size 128 kb 128 Mb 512 Mb 650 Mb Gb 30 Gb Non-volatile Z Z x Z Z Z Write many Once Z Z Once Z Z Large bytes x x Z Z Z Cheap per bit x Z Z Z Fast access Z Z x x x 1 byte 8 bits 1 kb 1 kilobyte 1024 bytes 1 Mb 1 megabyte 1024 kb 1 Gb 1 gigabyte 1024 Mb Table Memory and data storage technologies 6