Advanced Teletext System User Guide

4 Teletext Operating System Commands
4.1 Introduction
This chapter is only of interest if you intend to write your own programs to
handle Teletext data.
The Teletext Operating System (OS) commands allow you access to the
facilities of Teletext from your own programs. Some of the commands should
be used with care because they copy Teletext data into the computer's
memory and if used incorrectly could corrupt your program. Certain of the
Terminal's facilities, such as REVEAL, are not available as OS commands.
These have to be implemented by your program if you wish to use them.
Important: Before you use the Teletext OS commands you must issue a
*TTXON command (see below) to tell the Teletext Adaptor to start accepting
Teletext data. When you have finished with Teletext, issue a *TTXOFF
command to turn of the Adaptor's Teletext reception. This is important, as the
computer's memory may be corrupted by unexpected data arriving from the
Adaptor.
4.2 The Commands
All the commands can be typed in from the keyboard or included in a BASIC
program. Each command is described separately under the following
headings:
Description What the command does in functional terms.
Syntax The actual command words and the order in which commands
and data are arranged.
Example An example of a string of commands including the one described.
Note Additional information.
As with any other BBC Microcomputer OS command, Teletext allows you to
type abbreviations for its commands, such as *TE. for *TELETEXT, or
*MAG. for *MAGAZINE.
To avoid clashes of OS command names, the Teletext system allows an extra '
T' to be placed before a command, e.g. *TTIME for *TIME, or *TPAGE for
*PAGE.
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