Data Output
Going back to the word processor, the characters must be displayed on the screen as they are typed in, so the character codes stored in memory are also sent to the screen via the graphics interface. The display is made up of single colored dots (pixels) organized in lines across the screen, which are accessed in sequence, forming a scanned display. The shape of the character on screen must be generated from its code in memory, and sent out on the
correct set of lines at the right time. The display must therefore be created as a two- dimensional image made up from a serial data stream which sets the color of each pixel on the screen in turn, line by line, where each line of text occupies a set of adjacent lines.
The exact arrangement depends on the font type and size.
If a file is transferred on a network, it must also be sent in serial form. The characters (letters) in a text file are normally sent as ASCII code, along with formatting information and network control codes. ASCII code represents one character as one byte (8 bits) of binary code, and is therefore a very compact form of the data. The code for the letter ‘A’ (upper case), for example, is 01000001.
The printer works in a similar way to the screen, except that the output is generated as lines of dots of ink on a page. In an inkjet printer, you can see the scanning operation
taking place. These days, printer data is usually transferred in serial form on a USB, wireless or network link. The printer itself is capable of formatting the final output; only the character code and any formatting codes are needed. A portable document format (PDF) file is a standard output format for the display and printing of documents containing text and graphics.
The operation of the word processor can be illustrated using a flowchart, which is a graphical method of describing a sequential process. Figure 1.5 shows the basic process of text input and word wrapping at the end of each line. Flowcharts will be used later to represent microcontroller program operation.