NAUG Ch11 — Introduction to Hardware
Holmes & Dickens, The New Advanced User Guide, pp.157-161. Five-page chapter that frames the BBC system block diagram and tabulates the SHEILA memory map across all machines in the range.
Mostly recapped elsewhere. The chapter’s primary contribution to the wiki is the consolidated SHEILA table showing which chips live at which offsets across Model B, B+, Master, Compact, and Electron.
Key facts captured (vs what’s already in the wiki)
- System block diagram (§p151) — the CPU plus three buses (data, address, control), with peripherals memory-mapped into the address space.
- 6502 / 65C12 generic family — both chips referred to as just “6502” throughout the rest of the book.
- 16-bit address bus → 64 KB max. Data bus bidirectional, address bus unidirectional (with video circuit exceptions allowing 6845 / 5050 to provide addresses for RAM fetches).
- Page
&FE(SHEILA) holds the system hardware registers;&FC(FRED) and&FD(JIM) are for the 1 MHz expansion bus / cartridges (memory-map). - Co-processors connect via the Tube — Ch18 (separately ingested).
Extra SHEILA assignments not previously captured
Per the consolidated table on §p154:
| Offset | Chip | Machine availability |
|---|---|---|
&00-&0F | Electron ULA (various hardware functions) | Electron only |
&18 | Econet station number | Master, Compact |
&18-&1A | µPD7002 ADC | Electron only |
&24 | Floppy disc control register | Master, Compact |
&28 | WD1770 FDC | Master, Compact |
&38 | INTOFF — Network NMI disable | B+, Master |
&3C | INTON — Network NMI enable | B+, Master |
Note: on Master / Compact, the ADC moves from &FEC0-&FEDF (B/B+) to &FEC0- (with the Econet interface sharing that range on those machines).
Filed into
- memory-map — SHEILA table updated with the above entries.
Open follow-ups
None — this chapter is summary material whose detail lives in the dedicated per-chip chapters (Ch12 memory, Ch13 video, Ch15 serial, Ch20 ADC, Ch22 VIAs, Ch23 1 MHz bus, etc.).
This wiki is curated by Claude following the LLM-Wiki methodology — a human curates source documents, the LLM compiles structured cross-linked markdown. Content may contain errors, omissions, or stale claims. For authoritative information refer to the original source documents in the bbc-documents GitHub archive.