Acorn System 2 Technical Manual
The System 2 Technical Manual is Acorn Computers' assembly and reference manual for the Acorn System 2, issue 1, dated January 1980. The hosted copy is not a scan. It is a plain-text transcription made by Ben Harris, who OCRed the printed manual and converted it to text in April 1998 and published it in his Acorn archive.[1] His text was set as a 38-page A4 PDF for RetroTechCollection without changes to the wording, and a header on the first page records the source.[2] Chris Whytehead's Chris's Acorns points to Ben Harris's site for the manual.[3]
The manual covers the four-card System 2: the 6502 CPU card (200,000), the cassette interface (200,001), the VDU interface (200,002) and the memory card (200,003), with the backplane and the Eurocard frame. Chapters 2 to 4 are for building the system from a kit.[2]
Contents
[edit | edit source]Acorn's chapter list, with the printed page numbers carried in the transcription and the page numbers of the PDF:
| Chapter | Title | Printed pages | PDF pages |
|---|---|---|---|
| 1 | Introduction | 1-1 | 2 |
| 2 | Parts list (CPU, cassette interface, VDU interface and memory cards, backplane and frame) | 2-1 to 2-4 | 3-6 |
| 3 | Electrical assembly (technique, then each card and the backplane) | 3-1 to 3-12 | 7-17 |
| 4 | Mechanical assembly (card frame, card positions, guides) | 4-1 to 4-5 | 18-22 |
| 5 | Peripheral devices (power supply, keyboard, cassette recorder, display) | 5-1 to 5-4 | 23-26 |
| 6 | Cassette Operating System commands | 6-1 to 6-8 | 27-31 |
| 7 | Operating system control characters (screen editor, printer and screen control) | 7-1 to 7-4 | 32-34 |
| 8 | Teletext visual display unit (display control codes) | 8-1 to 8-4 | 35-38 |
| 9 | O.S. software specification | Not transcribed | |
| 10 | Circuit diagrams and descriptions | Not transcribed | |
| 11 | System expansion | Not transcribed | |
What it settles
[edit | edit source]- The card set and the parts on each card, with the capacitor values (pp. 2-1 to 2-4). Each card has one electrolytic: 15 µF on the CPU, cassette and memory cards, and 10 or 15 µF at C1 on the VDU card. On the CPU card the parts list puts it at C9, while the assembly text puts it at C8 (p. 3-6). 47 nF parts may replace the 100 nF ceramics (p. 3-1).[2]
- How the System 1 CPU card is set up for the System 2: IC5, IC6 and the regulator IC13 are not fitted, C10 is not used, the COS ROM goes in IC7 with a track cut and a link on the address selection pads, and three wires join IC2 to the backplane for the cassette signals (pp. 3-6 to 3-8).[2]
- The memory card: 4 KB of 2114 RAM in IC3 to IC10 with a link at RAM 1, sockets for a further 4 KB, and BASIC in IC17 (issue 2 card) or in two EPROMs in IC17 and IC18 (issue 1), with a link at ROM 6 (p. 3-10).[2]
- The backplane: eight 64-way card sockets, the left-hand slot's isolated address bus, the four wire-wrapped links between the CPU and cassette cards, and the earth wire to the frame (pp. 3-11 and 3-12).[2]
- Power: a stabilised 5 V supply of at least 1.5 A, or 2 A with 8 KB of RAM, with a safety earth to the frame if the supply's 0 V is not earthed (p. 5-1).[2]
- The keyboard edge and header connections (pp. 5-1 and 5-2); the cassette levels of 300 mV RMS, set by R3 and R12, and over 2 V peak to peak unclipped at IC7 pin 7 (p. 5-3); the 1 V 75 Ω composite video on pin 15 and the R3 adjustment on the VDU card (pp. 5-3 and 5-4).[2]
- The "Acorn Cos" sign-on with its asterisk prompt, the "Com?" and "Syn?" responses, and the COS commands (chapter 6).[2]
What this transcription does not contain
[edit | edit source]- The pictures. Each one is marked "[ Picture removed from ASCII version ]", so the frame and backplane drawings, component positions, address link diagrams, resistor colour code chart and cassette and modulator wiring diagrams are missing.[2]
- Chapters 9 to 11, including the circuit diagrams and descriptions.[2] The CPU and cassette cards are System 1 boards, whose circuit diagrams are hosted as Acorn System 1 Circuit Diagrams.
- Voltage ratings. The parts lists give capacitance only.[2]
- Fault-finding. The manual has no troubleshooting section.[2]
- Acorn BASIC, which is described in its own manuals.[2]
The text is OCR output. Ben Harris marked one word he could not read ("???degree???", p. 3-4), and some characters are misread, such as "IC1O" for IC10 and "Cl" for C1 in the parts lists. Check a value against the context before relying on it.[2]
Pages that cite this document
[edit | edit source]- Acorn System 2: cards, power, display and cassette
- Acorn System 2 Maintenance Guide: parts lists, assembly, card positions and power
- Acorn System 2 Troubleshooting Guide: set-up links, power, cassette and display levels, COS messages
- Acorn System 2 Capacitor Replacement Guide: capacitor values and substitutions
- The Acorn System 3 and Acorn System 4 pages and guides: the same CPU, VDU and memory cards
Download: Acorn System 2 Technical Manual (text transcription).pdf
References
[edit | edit source]- ↑ Ben Harris, Acorn manuals archive: Sys2TM.txt (chapters 1 to 5, revision 1.11, 21 May 1998) and Sys2TM/ (chapters 6 to 8). Retrieved 2026-10-01.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 File:Acorn System 2 Technical Manual (text transcription).pdf, page 1 header and title page.
- ↑ Chris Whytehead, "Acorn System 2", Chris's Acorns, Centre for Computing History. Retrieved 2026-10-01.