Acorn Products Z80 Manual do Utilizador

4. Disassembly and assemblyTo service the Z80 second processor, disconnect it from the BBC Microcomputer and the mains supply and undo the t

5. Circuit DescriptionThe circuit may be split into a number of sections by their specific function. These are dealt with under separ

is detected. IC26 and IC27 provide a clock signal, NMISERV during such a cycle, which presets the ROM latch IC15A, latching the ROM in until an instru

signal to the CPU is a pulse of approx. 4µs duration, sufficient to produce a reset without delaying the refresh to the DRAMS and

Fig. 2 RAM read or write cyclesCAS is enabled if:i. the memory cycle is a write cycle (WR low, to IC20C pin 11).or ii. the memory cycle is a rea

Fig. 3 Instruction-Fetch cycles5.8 DRAM RefreshAfter each instruction-fetch, the Z80 CPU performs a Refresh cycle for the DRAMS in the period whi

memory control signals go active. The Refresh address is incremented by the CPU after each time.Once the MREQ signal goes active, the "D&qu

5.10 The TubeThe Tube (IC1) is an Acorn custom IC which provides parallel asynchronous communication between two processor systems, th

Fig. 6 Schematic diagram of Tube registers

The fo11owing tables show the relative address and type of each register in the Tube, firstly for the Host system, and secondly for

As can be seen from Fig. 6 and Tables 1 and 2, each numbered register (e.g. register 1) is actually two registers, one for reading and one for writin

DESCRIPT1ON OF PINS (ref. Fig.7):Power Supply GND 0V supply railVCC1Parasite main +5V supplyVCC2Parasite secondary supply (+2-3v)VCC3Host +5V supplyDa

5.10.3 Tube Timing DiagramFig. 8 Tube Timing DiagramN.B.The timing reference for the Post is 0 and R/W gives the direction of transfer.For the parasit

6. Fault Finding on the Z80 Second Processor6.1 Generala) The Z80 second processor has three socketed IC's (IC 1 - 3) - these may easily be repla

"BBC Microcomputer 32k..." message displayed.Predominantly caused by either power failure, misconnected or damaged plugs and/or interconnect

6.3 Circuit Checks6.3.1 ClockUsing an oscilloscope, check that a 12MHz signal is being generated at pin 13 of IC22D. If not, check the crystal X1,

If WAIT is permanently low, or high, check TP7 after pressing BREAK; the WAIT signal should go low and then high. If not, check that (0) is clocking I

6.3.5 Desynchronising Logic and PCS Disable HCSAfter power-up, check that PCS is active at pin 18 of IC1. If not, then either the Tube 1C

address lines are shorted together and that all data lines are operating and not tied together.6.3.9 Power SupplyCheck the 250 mA. type T mains fuse,

Fig. 9 Position of +5V Trimmer on Power Supply PCB.If the current is zero, the second processor PCB has gone open circuit. Check fuse FS1 a

Z80 SECOND PROCESSSOR SERVICE MANUALPart No. 0409,015 Issue 2August 1984

Diagnostic FlowchartsNote: The letters in circles refer to the relevant flowcharts which follow.Master Flowchart

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Within this publication the term 'BBC' is used as an abbreviation for 'British Broadcasting Corporation'.°Copyright Acorn Computer

Power Supply3 5

Z80 Second Processor Functional Block Diagram

Z80 second Processor PCB Circuit Diag

Z80 PCB Silk Screen43

CONTENTSPage1 Introduction 12Packaging and Installation23Specification34 Disassembly and Assembly 45 Circuit Description 55.1 CPU55.2 Clock55.3 ROM La

Power Supply Circuit Diagram

Z80 Second Processor General Assembly47

Z80 Second Processor Parts ListsNOTE: Items indentified by * are norma11y available as spare parts - please contact your supplier for de

Z80 PCB Assembly (SEE PAGE 41) - cont'd31704,164 * INTEGRATED CIRCUIT 8264 8 IC6-1332742,123 * INTEGRATED C1RCUIT 74LS123 1IC1433 741,074/ 1NTEGR

WARNING: THE Z80 SECOND PROCESSOR MUST BE EARTHEDImportant: The wires in the mains lead for the. Z80 second processor are coloured in accordance with

1. IntroductionThis manual is intended to provide the information required to diagnose and repair faults on the Z80 second processor (a part

2. Packaging and Installation.The Z80 second processor is supplied in a two-part moulded polystyrene packing which is further packaged within a car

3. Specification3.1 The Z80 second processorA second processor for the BBC Microcomputer model B, operating through the Tube, providing the a