Introduction

This document is an attempt to specify the XBRA protocol for exception vector chaining on the atariST series of computers. It is a response to many requests I have received to document the protocol, and also an encouragement for people grabbing exception vectors to use it. This protocol was not invented by me, nor is it perfect for every situation, but still is very useful because something is better than nothing. There have been other proposals, but IMHO this is the simplest and cleanest, and does the job for which it was designed quite well. It has been used quite widely, especially in Public Domain circles, and that is a good enough reason for me to follow it.