BBC Microcomputer Service Manual Oct 1985 Section 1 BBC Micro ...

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1.2.3 Expansion The following expansion options are available, some of which may be fitted internally at purchase, but all of which could be fitted by Dealers at a later date:- * Floppy disc interface (fitted as an option at purchase) * Econet network interface (fitted as an option at purchase) * Voice synthesis circuit with cartridge ROM pack interface * Various alternative high-level languages in ROM External options which plug directly into the machine include:- * Games paddles * Cassette Recorder * Black and White and colour monitors and televisions * 5 1/4" disc drives, ranging from single-sided single density (100K) to dual double sided double track density (800K). * Dot-matrix or daisy wheel printers, serial or parallel interface * Teletext acquisition unit enabling Tele-software to be downloaded into the BBC Computer as well as providing access to the normal Teletext services. Pages may be "grabbed" and stored for later use. * 3 MHz 6502 second processor with 64K of RAM. * Z80 second processor with 64K of RAM and a fully CP/M-compatible operating system. * IEEE interface * Winchester 10 megabyte disc drive * Prestel adaptor unit 1.2.4 Software Considerable attention has been paid to the overall design of both systems and applications software. A modular approach has been adopted specifically to ease the interfacing of various high-level languages ( such as BASIC and Pascal) to the operating system. 1.2.5 Machine Operating System A 16K ROM is used for the MOS. This software controls all input/output devices using a well defined interface. The MOS supports the following interrupts (the full implementation only being available from MOS 1.2 onwards):- * Event Timer (10ms) (used as an elapsed time clock) * 4 channel analogue to digital converter * Vertical sync * Keyboard and keyboard buffer * Music tone generation and buffer * Serial interface, input and output buffers * Parallel input/output port and 'hooks' are provided to support other devices such as:- * Teletext acquisition * Prestel acquisition * Econet file system * Disk file system * Byte transfer to second processor The majority of the operating system calls are vectored to enable the user to change them if required. 4
1.2.6 BASIC The BASIC interpreter is an extremely fast implementation, with numerous powerful extensions:- * Long variable names * Integer, floating point and string variables * Multi-dimension integer, floating point and string arrays * Extensive support for string handling * IF ... THEN ... ELSE * REPEAT ... UNTIL * Multi-line integer, floating point and string functions * Procedures * Local variables * Full recursion on all functions and procedures * Effective error trapping and handling * Cassette loading and saving of programs and data * Full support for the extensive colour graphics facilities * Easy control of the built-in music generation circuits * Built-in 6502 mnemonic assembler enabling BASIC and assembler to be mixed, or pure assembly language programs to be produced. 1.3 Packaging The BBC Microcomputer is supplied in a two part moulded polystyrene packing which is further packaged within a cardboard sleeve. With the Microcomputer, a User's Manual, a Welcome Cassette package and a UHF TV lead are also supplied. The packaging should be kept intact in case it becomes necessary to transport the unit at a later date. 1.4 Mechanical assembly of case etc The lid of the Microcomputer case may be removed after undoing four fixing screws, two on the rear panel and two underneath. When reassembling, press the lid down at the rear whilst tightening the two rear fixing screws. Take care not to lose the two spire clips pushed onto the case lid, into which the rear fixing screws locate. NB Do not remove the lid with the mains power connected. Inside the Microcomputer are three main sub-assemblies: power supply unit, keyboard and the main printed circuit board. To remove the keyboard, undo the two or, in some cases, three screws and nuts holding it to the case bottom, take care to note the positions of the associated washers. Unplug the 17 way keyboard connector and the 2-way loudspeaker connector from the main printed circuit board, and the 10 way serial-ROM connector, if fitted. The power supply unit is connected to the main circuit board by seven push-on connectors which may be unplugged. Three screws on the underside of the case are undone allowing the unit to be removed. On reassembly, ensure that the same type of screw is used. The main printed circuit board can be removed after the two wires to SK2 (composite video BNC socket) have been disconnected. Undo the four fixing screws (five or seven screws on later issue boards) and remove the circuit board from the case by sliding it forwards and then lifting it from the rear. 5
Page 3 and 4: BBC Microcomputer service manual SE
Page 5: SECTION 1 BBC Microcomputer Models
Page 8 and 9: 6 - Servicing + Fault-finding 6.1 I
Page 11 and 12: 1 Introduction 1.1 Nature and Purpo
Page 13: 1.2.2 Model B Specification The Mod
Page 17 and 18: In the other screen modes, the info
Page 19 and 20: 3. Detailed Circuit Description 3.1
Page 22 and 23: 3.3 CRT controller + video processo
Page 24 and 25: The row address strobe signal is pr
Page 26 and 27: The speed of printing on the screen
Page 28 and 29: The CRTC is still used to generate
Page 30 and 31: is also determined by the control r
Page 32 and 33: 3.9 A to D convertors A four channe
Page 34 and 35: 3.13 1 MHz bus The address and data
Page 36 and 37: ii) Insert the above ICs into the s
Page 38 and 39: Edge connector pin number |6|7|8|9|
Page 40 and 41: R39-100k R47-1k5 R61-1k0 ii) Solder
Page 42 and 43: 10. WEST selects 5 1/4" disc. EAST
Page 44 and 45: 32. WEST selects A 13 input to pin
Page 46 and 47: 5.3 Circuit Modifications from issu
Page 48 and 49: 6 Servicing and Fault-finding 6.1 I
Page 50 and 51: iii) Check for the presence of the
Page 52 and 53: * On a number of occasions, the tra
Page 54 and 55: 6.5 Test programs and sample wavefo
Page 56 and 57: The 'following shows two more trace
Page 58 and 59: 170 !(&3200 + offset%) = &4433283F
Page 60 and 61: 7 Interfacing Survey 7.1 Purpose of
Page 62 and 63: The other way in which the RS423 ca
Page 64 and 65:
The 20-way User Port is much simple
Page 66 and 67:
8 Component location tables The fol
Page 68 and 69:
8,2 Transistors Q Type Circuit Diag
Page 70 and 71:
8,5 Resistors R Value Circuit Diagr
Page 72 and 73:
116 3k9 14,2 117 2k2 14,2 118 1k0 1
Page 74 and 75:
6 4
Page 91 and 92:
9.8 Parts list CASE LOWER ASSEMBLY
Page 93 and 94:
65 631,047 CAPACITOR 47pF PLATE CER
Page 95 and 96:
9.9 Glossary of abbreviations ACK A
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BBC Microcomputer Service Manual Oct 1985 Section 1 BBC Micro ...

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