Acorn computer Z80 Second Processor Bedienungsanleitung
Z80 SECOND PROCESSSOR SERVICE MANUAL
Part No. 0409,015
Issue 2
August 1984
Within this publication the term 'BBC' is used as an abbreviation for
'British Broadcasting Corporation'.
°Copyright Acorn Computers Limited 1984
Neither the whole or any part of the information contained in, or the
product described in, this manual may be adapted or reproduced in any
material form except with the prior written approval of Acorn
Computers Limited (Acorn Computers).
The product described in this manual and products for use with it, are
subject to continuous development and improvement. All
information of
a technical nature and particulars of the product
and its use (
including the information and particulars in this manual) are given by
Acorn Computers in good faith. However, it is acknowledged that there
may be errors or omissions in this manual. A list of details of any
amendments or revisions to this manual can be obtained upon request
from Acorn Computers Technical Enquiries.
Acorn Computers welcome
comments and suggestions relating to the
product and this manual.
All correspondence should be addressed to:-
Technical Enquiries
Acorn Computers Limited
Newmarket Road
Cambridge
CB5 8PD
All maintenance and service on the product must be carried out by
Acorn Computers' authorised dealers. Acorn Computers can accept no
liability whatsoever for any loss or damage caused by service or
maintenance by unauthorised personnel. This manual is intended only to
assist the reader in the use of this product, and therefore Acorn
Computers shall not be liable for any loss or damage whatsoever
arising from the use of any information or particulars in, or any
error or omission in, this manual, or any incorrect use of the
product.
This manual is for the sole use of Acorn Computers' authorised dealers
and must only be used by them in connection with the product described
within.
First published 1984
Published by Acorn Computers Limited
CONTENTS
Page
1 Introduction 1
2
Packaging and Installation
2
3
Specification
3
4 Disassembly and Assembly 4
5 Circuit Description 5
5.1 CPU
5
5.2 Clock
5
5.3 ROM Latch
5
5.4
Wait-States 6
5.5 Reset
6
5.6 Interrupt Handling
7
5.7 DRAM Control
7
5.8 DRAM Refresh
9
5.9 Desynchronising Logic
10
5.10 The Tube
11
6
Fault Finding on the Z80 Second Processor
17
6.1
General 17
6.2 Fault Conditions
17
6.3
Circuit Checks 19
Appendix
Diagnostic Flowcharts
25
Z80 Second Processor - Block Diagram
37
Circuit Diagram
39
Z80 PCB - Component Layout
41
Silk-Screen 43
Power Supply Unit - Circuit Diagram
45
Z80 Second Processor - General Assembly
47
Parts Lists - General Assembly
49
Z80 PCB Assembly
49
WARNING: THE Z80 SECOND PROCESSOR MUST BE EARTHED
Important: The wires in the mains lead for the. Z80 second processor
are coloured in accordance with the following code:
Green and yellow
Earth
Blue
Neutral
Brown
Live
As the colours of the wires may not correspond with the coloured
markings identifying the terminals in your plug, proceed as follows:
The wire which is coloured green and ye11ow must be connected to the
terminal in the plug which is marked by the letter E, or by the
safety earth symbol 4 or coloured green, or green and ye11ow.
The wire which is coloured blue must be connected to the terminal
which is marked with the letter N, or coloured black.
The wire which is coloured brown must be connected to the terminal
which is marked with the letter L, or coloured red.
If the socket outlet available is not suitable for the plug
supplied,
the plug should be cut off and the appropriate plug
fitted and wired
as previously noted. The moulded plug which was
cut off must be-
disposed of as it would be a potential shock hazard if it were to be
plugged in with the cut off end of the mains cord exposed. The moulded
plug must be used with the fuse and fuse carrier firmly in place. The
fuse carrier is of the same
basic colour* as the coloured insert in the base of the plug. Different
manufacturers' plugs and fuse carriers are not
interchangeable. In the
event of loss of the fuse carrier, the moulded plug MUST NOT be used.
Either replace the moulded plug
with another conventional plug wired
as previously described, or
obtain a replacement fuse carrier from an
authorised BBC
Microcomputer dealer. In the event of the fuse blowing
it should
be replaced, after clearing any faults, with a 3 amp fuse
that is ASTA approved to BS1362.
*Not necessarily the same shade of that colour.
1. Introduction
This manual is intended to provide the information required to
diagnose and repair faults on the Z80 second processor (a part of the
BBC Microcomputer system) which was designed by Acorn Computers
Ltd.
of Cambridge, England.
The information contained in this manual is aimed at Acorn dealers and
service engineers who will be servicing the Z80 second processor on
behalf of Acorn Computers Ltd.
Z80 is a trademark of Zilog Inc.
CP/M® is a registered trademark of Digital Research Inc.
The Tube is a trademark of Acorn Computers Limited.
2. Packaging and Installation.
The Z80 second processor is supplied in a two-part moulded
polystyrene
packing which is further packaged within a cardboard
sleeve. Supplied
with the second processor is a DNFS ROM with fitting instruction
sheet, a set of reminder cards for the red function keys, 7 floppy
disks, an end-user licence and a guarantee card. For BBC
Microcomputers fitted with MOS ROMs below version 1.2, a voucher
redeemable against replacement of lower version
ROMs, is also
supplied.
Note: Care should be taken when unpacking and repacking this unit to
ensure that all items are positioned correctly, especia11y the floppy
disks which should first be packed in plastic bags and laid flat.
The Z80 Second Processor User Guide and accompanying literature is
supplied packed separately.
A mains power switch is located at the rear of the second processor.
A 250mA. type T (slow blow) fuse is located at the rear of the second
processor. Before removing this fuse, the second processor must be
disconnected from the mains supply. Access to the fuse may
be gained
by undoing the round cover with the slot in it using a
screwdriver.
The mains supply must not be reconnected until the fuse is relocated
in its holder with the cover screwed home.
Do not use the second processor in conditions of extreme heat, cold,
humidity or dust, or in places subject to vibration. Do not block the
ventilation under or behind the second processor. Ensure
that no
foreign objects are inserted through any openings in the
second
processor.
3. Specification
3.1 The Z80 second processor
A second processor for the BBC Microcomputer model B, operating
through the Tube, providing the ability to run sophisticated software
under the CP/M 2.2 operating system.
The second processor is housed in a rigid injection moulded
thermoplastic case and contains the fo11owing:
A 6MHz Z80B CPU
64K of read/write Random Access Memory
4K Read Only Memory ("shadow ROM") providing a boot function on power-
up and to handle Non-Maskable Interrupts (NMI) from the Host
processor
via the Tube.
The Tube - a fast asynchronous communication path connecting the
second processor to the I/O processor (BBC Microcomputer).
A mains-operated integral power supply comprising a mains transformer
and power supply board.
3.2 Power Supply
Max. AC Input
264V AC
MIN. AC Input 216V AC
Power Rating
14 watts
Supply Frequency
47-63Hz
Max. Output Current lA at +5V
4. Disassembly and assembly
To service the Z80 second processor, disconnect it from the BBC
Microcomputer and the mains supply and undo the three fixing screws;
two at the top of the back panel and one underneath the unit, nearest
the front and equidistant between the two rubber feet. (The assembly
diagram is given in the Appendix). The lid can now be removed
revealing the transformer and power supply
board, held in place by six
screws, and the Z80 PCB. It is recommended
that the transformer and power supply board are not removed unless
absolutely necessary.
To remove the Z80 PCB from the case, pu11 off the two "fast on" tabs
which connect the power supply (brown +5v and black 0v leads) and
remove the four screws which hold the PCB in place.
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