Acorn BBC Master 128, Service Manual

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Master Series Service Manual
5 Hardware description
5.1 Introduction
The Master Series Microcomputer consists of a central processing unit
with associated memory and various input/output devices for
communication with external equipment. Only a fully configured system
will be described here although reference to sub-systems will be made
where relevant.
The Core Machine
All input/output (I/O) computing is performed by a 65C12 CPU with its
principal ancillary components:-
128 Kbyte of Dynamic Random Access memory:- Special expansion options
allow a further expansion of 64 Kbyte. Dedicated hardware can be used
to expand this almost indefinitely.
262 Kbyte of Read Only Memory:- Special expansion options allow a
further expansion of approximately 1/2 Mbyte of ROM. Plug in
cartridges are available which accept up to 256 Kbyte of ROM.
Internal I/O
Various I/O devices operate solely within the confines of the system
to either improve facilities or increase throughput. These are as
follows:-
6522 VIA devices - Two of these are provided and interface to:-
1) A 93 contact keyboard with 2 key rollover.
3-Channel sound generator with additional noise
channel. Battery backed up Real-Time Clock and fifty
bytes of RAM.
2) The Printer Port and User Port
Co-processors
These consist of an additional CPU with associated memory. They have
no I/O capability of their own and depend entirely on the main
processor to supply such information. They do all the computation not
associated with I/O operations.
When a co-processor is not fitted, the main processor has to perform
both I/O and non I/O computation.
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