Acorn Z80 Second Processor Documentation

Acorn's Z80 Second Processor documentation hosted here comprises the service manual, the user guide, the leaflet on preparing the BBC Micro, and Acorn's sales leaflet for the Acorn Z80 Second Processor.

Service manual

The Z80 Second Processor Service Manual is Acorn Computers' dealer service manual, part number 0409,015, issue 2, August 1984. The hosted PDF has 58 pages. Its text was retyped from the original and keeps OCR errors such as "1C" for "IC", "ye11ow", "PALF" for "half" and "Till" for TH1. The timing diagrams, flowcharts and drawings are scanned images.

**Service manual contents (printed pages)**
Section	Page
1 Introduction	1
2 Packaging and installation (DNFS ROM, seven discs, 250 mA type T rear fuse)	2
3 Specification: Z80B at 6 MHz, 64K RAM, 4K shadow ROM, power supply	3
4 Disassembly and assembly	4
5 Circuit description: CPU, clock, ROM latch, wait states, reset, interrupts, DRAM control and refresh, desynchronising logic, the Tube and its registers	5 to 16
6 Fault finding: general (socketed ICs, test points TP1 to TP9), fault conditions, circuit checks	17 to 23
Appendix: diagnostic flowcharts	25 to 35
Appendix: block diagram, circuit diagram, component layout, silk screen, power supply circuit diagram, general assembly, parts lists	37 to 50

What it settles

The power supply specification: 216 to 264 V AC, 47 to 63 Hz, 14 W, 1 A maximum at +5 V (section 3.2).
The power supply test: a 10 ohm 2.5 W load across the brown and black leads, 4.95 to 5.25 V with no more than 50 mV of noise, set with the trimmer on the power supply board; the Z80 board draws 600 to 800 mA (section 6.3.9).
The overvoltage crowbar: D3 (5.1 V zener), R11 and TH1 (C122F) blow FS1 (1 A fast blow) at about 6.1 V (section 6.3.9 and parts list).
The Tube ULA supply checks: pin 4 at 5 V from the BBC Micro, pin 2 at 5 V and pin 3 at 2 to 3 V from the second processor (section 6.3.10).
The power supply circuit (p. 45), the same as the 6502 Second Processor's: reservoir C1 4700 µF 16 V, output C5 47 µF 35 V, TIP42 pass transistor, trimmer VR1 "set 5V" and a 1 A output fuse.
The main board polarised capacitors (parts list, p. 49): C2 100 µF 6.3 V and C3 47 µF 10 V electrolytics and C10 10 µF 35 V tantalum.

What it does not contain

Only the right-hand part of the main board circuit diagram (p. 39) is in the scan: the clock driver, wait state, DRAM control, NMI decode, boot ROM and DRAM sections. The Tube ULA, Z80, crystal oscillator and crowbar side of the drawing is missing.
The scanned drawings are 150 dpi and some labels are hard to read.
Two figures disagree within the manual. The reset pulse from IC14 is "approx. 4µs" in section 5.5 and "approximately 10µs" in section 6.3.4. The power supply limits are 4.95 to 5.25 V in section 6.3.9 and 4.9 to 5.1 V on the power supply flowchart, which also gives the board current as 700 mA ± 100 mA.
Section 6.3.1 places the 12 MHz signal at IC22D pin 13, while section 5.2 says the oscillator is built from IC24D and E.
No component data for the transformer or the power supply board beyond the circuit diagram; the parts list gives the supply as assembly 831,000.

User guide

Z80 second processor for the BBC Microcomputer User guide, part number 409010, issue 1, February 1984, written by Baddeley Associates. The hosted scan has 60 pages with a text layer. It covers the BBC Microcomputer Z80 pack (p. 7), setting up (pp. 8 to 19), files and filenames, using CP/M and its commands (pp. 20 to 37), the software in the pack (pp. 38 to 44), backing up, looking after discs and hardware (pp. 45 to 47) and CP/M error messages (p. 48). It gives the requirements (a Model B, MOS 1.2, DNFS, an 800K dual disc drive), the start-up banner "Acorn TUBE Z80 64K 1.0" and the CP/M banner "Acorn CP/M 2.2 - BIOS 1.0".

Preparing the BBC Microcomputer

Preparing the BBC Microcomputer for the Z80 Second Processor, part 409011, is a six-page leaflet packed with the unit. It explains how to check the MOS, DFS and NFS versions with *HELP (OS 1.20, DFS 1.20 and NFS 3.50 or later are needed), how to open the BBC Micro and swing the keyboard aside, and how to fit the MOS and DNFS ROMs. It warns that the Z80 will not work properly unless DNFS is the rightmost filing system ROM fitted.

Sales leaflet

The British Broadcasting Corporation Microcomputer Z80 Second Processor, leaflet AMP 06, January 1984, four pages. It lists the bundled software, says about 55K of the 64K RAM is free to user programs, and gives the configuration needed: a Model B with disc interface, MOS 1.2, a monitor or television, a dual 80-track disc drive and a printer. It gives the unit's size as about 205 × 345 mm.