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CHAPTER 5
Technical information for the user –
Firmware
This chapter assumes prior knowledge of the CPC464 firmware.
Some knowledge of the fundamentals of CP/M is also assumed. This chapter does not
however attempt to discuss the facilities available in the CP/M environment. Complete
information concerning CP/M, the CPC464 CP/M environment and the technical
specification of the BIOS is contained in SOFT159 A Guide to CP/M. The Complete
Firmware Specification of the Amstrad DDI-1 is contained in SOFT 158A, available
as an Appendix to the Concise Firmware Specification SOFT158.
5.0 Introduction
AMSDOS is a disc operating system for the AMSTRAD CPC464 fitted with the DDI-
1 floppy disc interface. AMSDOS enables BASIC programs to access disc files in a
similar manner to cassette files, indeed existing programs which currently use the
cassette should be able to use disc files with little, or no, modification. The main
source of incompatability will be file names in that, for AMSDOS, files names must
conform to CP/M standards whereas cassette file names are far less restricted.
AMSDOS has been designed to complement CP/M, not to compete with it. They share
the same file structure and can read and write each other's files. AMSDOS resides in
the same ROM as the CP/M BIOS.
AMSDOS switches the cassette input and output streams (#9) to and from disc. Thus
all the facilities available on cassette become available on disc. In addition displaying
the disc directory, erasing disc files, renaming disc files, and selecting the default
drive and user are also facilitated.
These facilities are implemented either by intercepting the cassette firmware calls or
by external commands.
5.1 Headers
Cassette files are subdivided into 2k blocks, each of which is preceded by a header.
CP/M files do not have headers. AMSDOS files may, or may not, have a header
depending on the contents of the file. This will not cause problems for programs
written in BASIC but is an important difference between cassette and disc files. This
could perhaps be exploited for a protection scheme.
Chapter 5. AMSTRAD Disc Drive & Interface DDI-1 Manual