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This graphics command is used to display a string of characters at a specified position, angle, slant, colour etc.

This concludes the basic description of the operation of the AVC and the software commands which are available to make it easy to use. In the next issue we will describe some applications of the AVC, and in particular we will introduce the first issue of NAS-CAD – a simple computer aided design system using the AVC.

2. Technical Tips

In this section we are introducing the first instalment of a series of articles on modifying the NAS-SYS operating system. While the features which we describe should be useful the intention of the series is to give some of the newer Nascom computer users an insight into the operating system and its features. The routines described have generally not been optimised for efficiency in respect of either speed or memory size.

2.1 A buffered keyboard for the Nascom computer

Buffered keyboards allow the user to type in information while the computer is still performing other tasks. They need to be used with care – if you type in answers to anticipated questions, but the actual questions from the program differ from those expected, the results can be disconcerting, to say the least! Keyboard buffers usually have a limited ‘type ahead’ capacity – typically 20 characters or less.

The keyboard buffering system which we are going to describe can be used with any non-networked Nascom 2 or 3 computer fitted with a PIO and running NAS-SYS 3 or NAS-DOS (and Nascom 1 computers, with a few minor changes to the procedure described). All that is required to fit it is a short length of wire, a soldering iron and a bit of software, so the cost is negligible. A shortcoming, though, is that the disc user will find the buffering is inoperative while disc access is in progress. This is because disc access disables the computers interrupt system, which we use in this buffering system. You will also find that the keyboard repeat speed is less consistent, and for games use in articular a type-ahead feature can be undesirable.

The keyboard buffering can be disabled at any time by use of the RESET key or restarting NAS-SYS (EO). The length of the keyboard buffer can be changed from within a program by POKing a single location (down to 1 if required).

The description that follows is intended for those who have some knowledge of their machine, or who want to know more about it. It gives all the information you need to implement the keyboard buffer. In future issues we will give some other technical tips which will build on the ideas presented here.