by Clive W. Humphris
Portable Learning, Reference and Revision Tools.
Copyright by eptsoft limited 2012
All rights reserved.
Our thanks and appreciation goes to John D. Ransley MIEE from Whitbourne in Worcestershire for all his help and expert guidance in developing this software title.
If you are looking for an easy and enjoyable way to improve your employability skills then our Brush Up series of eBooks is for you.
Published as an eBook version of fully interactive educational software published by eptsoft to schools, colleges and universities for over twenty years and now available as a portable, learning, reference and revision tools for students.
Details of how to download the free and highly interactive software to accompany this eBook can be found on the Additional Notes page below. Where all the colourful images shown in this eBook can be brought to life.
Educational software developed and published into schools and colleges worldwide for over twenty years.
Computer character codes are usually based on the ASCII (American Standard Code for Information Interchange). Originally this was a seven-bit code, but now provides an extended character set of 255 characters using eight bits. Computer keyboards are connected to the CPU via a serial interface whereby the individual codes are transmitted as binary strings. The keyboard encoder generates a unique code for each key press. Key presses are listed to enable comparisons to be made. Note the difference between upper and lower case characters (only one bit changed).
Within the character set there are special characters which are not displayed, i.e. tabbing, line feeds and backspacing.
The keyboard encoder is based on a matrix of rows and columns. At each intersection there is a switch, which is made for that key press. The generated binary code is produced from a look-up table. Speed is unimportant and transmission rates are limited to those of the fastest typist.
Within the encoder circuitry it is normal practice to continually scan the rows and columns on the keyboard for a user key press. These scans take place thousands of times between individual key presses. In this example some keys are inactive, i.e. function keys. This is because they are based on combinations of key codes and would only serve to confuse if included.