Analysis of a computer-controlled teletext decoder

Abstract

This thesis gives a deep insight into how a computer-controlled teletext decoder functions. It analyses a system based on the widely used SAA5243 Enhanced Computer Controlled Teletext chip in conjunction with the Video Interface Processor SAA5231. The SAA5231 is responsible for extracting the teletext data from the composite video and converting it to the required data levels. The SAA5243 performs all the data handling - namely data acquisition (i.e. accepting only that data corresponding to the page requested by the user) and character generation (i.e. converting received teletext binary data into legible output). It also incorporates an I2C interface and a memory interface. All communication between the PC and the SAA5243 follows the I2C-bus protocol. This is responsible for setting the ECCT registers which initialise the ECCT, determine the mode of operation and carry the information required for page capturing.