The Amstrad CPC Firmware Guide

Originally by Bob Taylor and Thomas Defoe, 1992
Electronic version scanned and formatted by David Cantrell, 1994


Computer programming is one of the most satisfying hobbies as it is a rare opportunity to invent, develop, and test your own ideas and see them come to fruition. Competent programming is a skill which is not easy to master, but once learnt, it will give hours of pleasure - there are many people who spend hours inventing new coding tricks, solving complex problems, or just trying out an idea.

Fortunately, when Amstrad developed the CPC and PLUS computers, they let the user access many of the computer's routines and use the Firmware in their own programs. Experienced programmers will no doubt write faster routines which are more efficient, or have some special feature, yet these extra facilities can easily be patched in using the Firmware Jumpblock.

For many years, Amstrad produced the definitive guide to the insides of the CPC but sale of this was stopped almost 3 years ago. [Note - 3 yrs ago means 1989 here]. Since then the Firmware Manual has been regarded as an antique by those who are fortunate enough to own a copy. Nevertheless, the original guide had some omissions, notably the abscence of information on the system variables and the Z80 microprocessor inside every CPC or Plus.

This guide is not intended to explain how to program in machine code, but we hope that it will supply the information needed to make the most of the Amstrad's capabilities when writing your own programs.

Bob Taylor and Thomas Defoe, 1992


This version of the firmware guide is based upon the ASCII version by David Cantrell with the following changes:

  • I removed the last sections with the Z80 instruction sets and CRTC registers.
  • Cross linked with SOFT968.
  • Fixed some typos/errors.

Here are the original ASCII and PDF versions of the Firmware guide:

  • ASCII version by David Cantrell, 1994.
  • PDF version by John Kavanagh, 2002
    (Note: I disabled the annoying security permission prohibiting the copying of the text in the original PDF).

documentations/firmware/guide/start.txt · Last modified: 2009/06/17 15:42 by grim