BBC Micro Model A/B - Revision history

Josh: Link the R. B. Coats BBC BASIC textbook and label it plainly as third-party with no hardware content

2026-09-25T01:31:53Z

Link the R. B. Coats BBC BASIC textbook and label it plainly as third-party with no hardware content

← Older revision		Revision as of 02:31, 25 September 2026
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	* [[BBC Micro Model A/B Capacitor Replacement Guide]]		* [[BBC Micro Model A/B Capacitor Replacement Guide]]
	* [[BBC Micro Model B+]]		* [[BBC Micro Model B+]]
			* [[BBC BASIC]] — R. B. Coats, Edward Arnold, 1983. A '''third-party textbook''' that states on its own title page that it "is in no way connected with either the BBC or the manufacturers of the computer, Acorn". No hardware content at all — not a source for any figure on this wiki.
	* [[Acorn Electron]]		* [[Acorn Electron]]
	* [[Recommended Tools]]		* [[Recommended Tools]]

Josh: Rewrite against the hosted BBC Microcomputer Service Manual (Oct 1985). Corrected: ULA is Uncommitted not Unified and there are two (video 5C094 IC6, serial 2C199 IC7); mode 2 has 16 logical colours not 8; modes 0,1,4,5 are 32 text rows not 25; modes 3 and 6 are text-only; there are no ROM cartridge slots, only four internal sideways ROM sockets; ROM is 16K MOS plus 16K language plus four paged sockets, not 32K total; cassette is 300 or 1200 baud. Removed unsourced dimensions, weight and 7-oc...

2026-09-23T01:56:37Z

Rewrite against the hosted BBC Microcomputer Service Manual (Oct 1985). Corrected: ULA is Uncommitted not Unified and there are two (video 5C094 IC6, serial 2C199 IC7); mode 2 has 16 logical colours not 8; modes 0,1,4,5 are 32 text rows not 25; modes 3 and 6 are text-only; there are no ROM cartridge slots, only four internal sideways ROM sockets; ROM is 16K MOS plus 16K language plus four paged sockets, not 32K total; cassette is 300 or 1200 baud. Removed unsourced dimensions, weight and 7-oc...

Show changes

Josh: /* 🧪 Related Pages */

2025-09-04T23:42:30Z

🧪 Related Pages

← Older revision		Revision as of 00:42, 5 September 2025
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	</gallery>		</gallery>

	== 🧪 Related Pages ==		== Related Pages ==
	* [[BBC Micro Model A/B General Maintenance]]		* [[BBC Micro Model A/B General Maintenance]]
	* [[BBC Micro Model A/B Troubleshooting Guide]]		* [[BBC Micro Model A/B Troubleshooting Guide]]

Josh at 20:27, 9 August 2025

2025-08-09T20:27:49Z

← Older revision		Revision as of 21:27, 9 August 2025
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	The '''BBC Microcomputer System''' (commonly known as the '''BBC Micro''') was a series of microcomputers designed and built by Acorn Computers Ltd for the BBC Computer Literacy Project. Launched in late 1981, it became a defining educational and home computer in the UK, renowned for its robust design, expandability, and role in British computing history.		The '''BBC Microcomputer System''' (commonly known as the '''BBC Micro''') was a series of microcomputers designed and built by Acorn Computers Ltd for the BBC Computer Literacy Project. Launched in late 1981, it became a defining educational and home computer in the UK, renowned for its robust design, expandability, and role in British computing history.

	== 🧠 Architecture and Processor ==		== Architecture and Processor ==
	At its heart, the BBC Micro employed the '''MOS Technology 6502A''' 8-bit microprocessor, clocked at 2 MHz. The system architecture was designed for flexibility and performance, with a fast system bus and a highly modular layout supporting a wide range of expansion options.		At its heart, the BBC Micro employed the '''MOS Technology 6502A''' 8-bit microprocessor, clocked at 2 MHz. The system architecture was designed for flexibility and performance, with a fast system bus and a highly modular layout supporting a wide range of expansion options.

Line 34:		Line 34:
	* '''Custom ULA''': Unified Logic Array for video, keyboard, and I/O timing		* '''Custom ULA''': Unified Logic Array for video, keyboard, and I/O timing

	== 💾 Memory and Storage ==		== Memory and Storage ==
	The BBC Micro was available in two main variants:		The BBC Micro was available in two main variants:
	* '''Model A''': 16 KB RAM		* '''Model A''': 16 KB RAM
Line 49:		Line 49:
	* '''ROM cartridge slots''' for instant software loading		* '''ROM cartridge slots''' for instant software loading

	== 🖥️ Display and Graphics ==		== Display and Graphics ==
	Graphics and video output were handled by a custom ULA and Motorola 6845 CRTC, supporting a range of text and graphics modes:		Graphics and video output were handled by a custom ULA and Motorola 6845 CRTC, supporting a range of text and graphics modes:

Line 75:		Line 75:
	* '''Hardware scrolling''', cursor, and palette controls.		* '''Hardware scrolling''', cursor, and palette controls.

	== 🔊 Sound Capabilities ==		== Sound Capabilities ==
	Audio was provided by the '''Texas Instruments SN76489''' programmable sound generator, offering:		Audio was provided by the '''Texas Instruments SN76489''' programmable sound generator, offering:
	* '''3 tone channels''' (independent pitch and volume)		* '''3 tone channels''' (independent pitch and volume)
Line 84:		Line 84:
	The BBC Micro's sound system was widely used in educational software, games, and music applications.		The BBC Micro's sound system was widely used in educational software, games, and music applications.

	== 🎮 Input/Output and Expansion ==		== Input/Output and Expansion ==
	The BBC Micro was designed for expandability, with a comprehensive set of I/O ports and internal connectors:		The BBC Micro was designed for expandability, with a comprehensive set of I/O ports and internal connectors:

Line 100:		Line 100:
	The Model B included all ports as standard; Model A required upgrades for some interfaces.		The Model B included all ports as standard; Model A required upgrades for some interfaces.

	== 🔍 PCB Schematics & Service Manual ==		== PCB Schematics & Service Manual ==
	The BBC Micro featured a robust motherboard design, with separate logic and power supply boards in most models.		The BBC Micro featured a robust motherboard design, with separate logic and power supply boards in most models.

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	Full service manuals and schematics are available at [[BBC Microcomputer Service Manual October 1985]]		Full service manuals and schematics are available at [[BBC Microcomputer Service Manual October 1985]]

	== 📷 Gallery ==		== Gallery ==
	<gallery mode="packed" heights="200">		<gallery mode="packed" heights="200">
	File:BBC Micro Front Restored.jpg\|BBC Micro Model B (front view)		File:BBC Micro Front Restored.jpg\|BBC Micro Model B (front view)

Josh: /* 🔍 PCB Schematics & Service Manual */

2025-05-09T20:19:03Z

🔍 PCB Schematics & Service Manual

← Older revision		Revision as of 21:19, 9 May 2025
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	{\| class="wikitable styled-table" style="width:80%; text-align:center;"		{\| class="wikitable styled-table" style="width:80%; text-align:center;"
	! ~~style="background-color:#f2f2f2;"\|~~ Logic Board		! Logic Board
	! ~~style="background-color:#f2f2f2;"\|~~ Logic Board Schematic		! Logic Board Schematic
	\|-		\|-
	\| [[File:BBC Micro Motherboard.jpg\|center\|thumb\|321x321px\|BBC Micro Model B Logic Board]]		\| [[File:BBC Micro Motherboard.jpg\|center\|thumb\|321x321px\|BBC Micro Model B Logic Board]]

Josh at 20:18, 9 May 2025

2025-05-09T20:18:39Z

← Older revision		Revision as of 21:18, 9 May 2025
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	{\| class="wikitable styled-table" style="width:80%; text-align:center;"		{\| class="wikitable styled-table" style="width:80%; text-align:center;"
	! style="background-color:#f2f2f2;"\| Logic Board		! style="background-color:#f2f2f2;"\| Logic Board
	! style="background-color:#f2f2f2;"\| ~~Power Supply~~ Board		! style="background-color:#f2f2f2;"\| Logic Board Schematic
	\|-		\|-
	\| [[File:~~BBC_Micro_Motherboard~~.jpg\|thumb\|~~center\|350px~~\|BBC Micro Model B Logic Board~~]][[File:BBC_Micro_Schematic.png\|center\|thumb\|BBC Micro Model B Schematic~~]]		\| [[File:BBC Micro Motherboard.jpg\|center\|thumb\|321x321px\|BBC Micro Model B Logic Board]]
	\| [[File:~~BBC_Micro_PSU.jpg\|thumb\|center\|350px\|~~BBC Micro ~~Power Supply Unit]][[File:BBC_Micro_PSU_Schematic~~.png\|center\|thumb\|BBC Micro ~~PSU~~ Schematic]]		\| [[File:BBC Micro Schematic.png\|center\|thumb\|350x350px\|BBC Micro Model B Schematic]]
	\|}		\|}
			Full service manuals and schematics are available at [[BBC Microcomputer Service Manual October 1985]]
	* Full service manuals and schematics are available at ~~the~~ [~~https://archive.org/details/bbc-micro-service-manual~~ BBC ~~Micro~~ Service Manual ~~(archive.org)~~].

	== 📷 Gallery ==		== 📷 Gallery ==
	<gallery mode="packed" heights="200">		<gallery mode="packed" heights="200">
	File:~~BBC_Micro_Front_Restored~~.jpg\|BBC Micro Model B (front view)		File:BBC Micro Front Restored.jpg\|BBC Micro Model B (front view)
	File:~~BBC_Micro_Rear~~.jpg\|Rear panel with I/O ports		File:BBC Micro Model B rear ports.jpg\|Rear panel with I/O ports
	File:~~BBC_Micro_Keyboard.jpg\|Keyboard close-up~~		File:BBC Micro Motherboard.jpg\|BBC Micro Model B motherboard
	~~File:BBC_Micro_Motherboard~~.jpg\|BBC Micro Model B motherboard
	~~File:BBC_Micro_PSU.jpg\|BBC Micro power supply~~
	</gallery>		</gallery>

Josh at 20:12, 9 May 2025

2025-05-09T20:12:59Z

← Older revision		Revision as of 21:12, 9 May 2025
Line 52:		Line 52:
	Graphics and video output were handled by a custom ULA and Motorola 6845 CRTC, supporting a range of text and graphics modes:		Graphics and video output were handled by a custom ULA and Motorola 6845 CRTC, supporting a range of text and graphics modes:

	{\| class="wikitable styled-table" style="width:80%; text-align:center;"		{\| class="wikitable styled-table" style="width:70%; text-align:center;"
	! Mode !! Resolution !! Colours !! Text Columns × Rows		! Mode !! Resolution !! Colours !! Text Columns × Rows
	\|-		\|-

Josh: /* 🧪 Related Pages */

2025-05-09T20:12:32Z

🧪 Related Pages

← Older revision		Revision as of 21:12, 9 May 2025
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	\| os = Acorn MOS (Machine Operating System) in ROM		\| os = Acorn MOS (Machine Operating System) in ROM
	\| predecessor = [[Acorn Atom]]		\| predecessor = [[Acorn Atom]]
	\| successor = [[BBC ~~Master Series~~]]		\| successor = [[BBC Micro Model B+]]
	\| codename = Proton		\| codename = Proton
	\| model = Model A, Model B, Model B+		\| model = Model A, Model B, Model B+
	\| logo = [[File:~~BBC Micro logo~~.svg\|250px]]		\| logo = [[File:BBC_Micro_Logo.svg\|250px]]
	}}		}}

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	== 🧪 Related Pages ==		== 🧪 Related Pages ==
	* [[BBC Micro General Maintenance]]		* [[BBC Micro Model A/B General Maintenance]]
	* [[BBC Micro Troubleshooting Guide]]		* [[BBC Micro Model A/B Troubleshooting Guide]]
	* [[BBC Micro Keyboard Repair Guide]]		* [[BBC Micro Keyboard Repair Guide]]
	* [[BBC Micro Capacitor Replacement Guide]]		* [[BBC Micro Model A/B Capacitor Replacement Guide]]
	* [[BBC Micro ROM Upgrades]]		* [[BBC Micro ROM Upgrades]]
	* [[BBC Micro Tube Expansion Guide]]		* [[BBC Micro Tube Expansion Guide]]

Josh: Automated update by bot

2025-05-09T20:09:11Z

Automated update by bot

New page

{{Infobox computer
| name = BBC Micro Model A/B
| image = [[File:BBC_Micro_Front_Restored.jpg|250px]]
| caption = BBC Micro Model B
| manufacturer = Acorn Computers Ltd
| type = Home Computer
| release date = 1 December 1981
| discontinued = 1986
| price = Model A: £235, Model B: £335 (1981, inc. VAT)
| cpu = MOS Technology 6502A @ 2 MHz
| memory = Model A: 16 KB RAM, Model B: 32 KB RAM; 32 KB ROM (BASIC, MOS, DFS)
| storage = Cassette tape, optional 5.25" floppy disk (DFS), ROM cartridge
| display = Teletext, 640×256 (monochrome), 320×256 (4 colours), 160×256 (8 colours), 80×25 text
| sound = Texas Instruments SN76489: 3 sound channels + 1 noise channel
| dimensions = 40 cm × 34 cm × 8 cm
| weight = 4.5 kg
| os = Acorn MOS (Machine Operating System) in ROM
| predecessor = [[Acorn Atom]]
| successor = [[BBC Master Series]]
| codename = Proton
| model = Model A, Model B, Model B+
| logo = [[File:BBC Micro logo.svg|250px]]
}}

The '''BBC Microcomputer System''' (commonly known as the '''BBC Micro''') was a series of microcomputers designed and built by Acorn Computers Ltd for the BBC Computer Literacy Project. Launched in late 1981, it became a defining educational and home computer in the UK, renowned for its robust design, expandability, and role in British computing history.

== 🧠 Architecture and Processor ==
At its heart, the BBC Micro employed the '''MOS Technology 6502A''' 8-bit microprocessor, clocked at 2 MHz. The system architecture was designed for flexibility and performance, with a fast system bus and a highly modular layout supporting a wide range of expansion options.

Key features:
* '''CPU''': MOS 6502A @ 2 MHz
* '''System bus''': 8-bit data, 16-bit address (64 KB address space)
* '''ROM''': 32 KB (split between BASIC II, Acorn MOS, and optionally DFS or other utilities)
* '''Custom ULA''': Unified Logic Array for video, keyboard, and I/O timing

== 💾 Memory and Storage ==
The BBC Micro was available in two main variants:
* '''Model A''': 16 KB RAM
* '''Model B''': 32 KB RAM (most popular)

Both models included 32 KB of ROM, containing:
* '''Acorn MOS''' (operating system)
* '''BBC BASIC II'''
* Optional: Disc Filing System (DFS) or other ROMs in cartridge slots

'''Storage options:'''
* '''Cassette tape interface''' (standard, 1200 baud)
* '''5.25" floppy disk drive''' (optional, via DFS)
* '''ROM cartridge slots''' for instant software loading

== 🖥️ Display and Graphics ==
Graphics and video output were handled by a custom ULA and Motorola 6845 CRTC, supporting a range of text and graphics modes:

{| class="wikitable styled-table" style="width:80%; text-align:center;"
! Mode !! Resolution !! Colours !! Text Columns × Rows
|-
| 0 || 640×256 || 2 (monochrome) || 80 × 25
|-
| 1 || 320×256 || 4 || 40 × 25
|-
| 2 || 160×256 || 8 || 20 × 25
|-
| 3 || 640×256 || 2 (monochrome) || 80 × 25 (text only)
|-
| 4 || 320×256 || 2 || 40 × 25
|-
| 5 || 160×256 || 4 || 20 × 25
|-
| 6 || 320×256 || 2 || 40 × 25 (reduced memory)
|-
| 7 || Teletext (Mode 7) || 8 (Teletext) || 40 × 25
|}

* '''Teletext Mode 7''': Hardware support for the UK's teletext broadcast standard, enabling high-quality text and simple graphics.
* '''Hardware scrolling''', cursor, and palette controls.

== 🔊 Sound Capabilities ==
Audio was provided by the '''Texas Instruments SN76489''' programmable sound generator, offering:
* '''3 tone channels''' (independent pitch and volume)
* '''1 noise channel'''
* 7-octave range
* Internal speaker (mono), with line-level output

The BBC Micro's sound system was widely used in educational software, games, and music applications.

== 🎮 Input/Output and Expansion ==
The BBC Micro was designed for expandability, with a comprehensive set of I/O ports and internal connectors:

* '''User port''' (8-bit parallel, TTL-level)
* '''Printer port''' (Centronics parallel)
* '''RS-423 serial port''' (for modems, printers)
* '''Analogue port''' (joysticks, ADC)
* '''RGB, composite, and UHF video outputs'''
* '''Cassette interface'''
* '''Econet network port''' (optional)
* '''Tube interface''' (for second processor expansion, e.g., 6502, Z80, 32016, ARM)
* '''1 MHz bus''' (for peripherals such as ADC, IEEE-488, etc.)
* '''ROM cartridge sockets''' (up to 4 sideways ROMs)

The Model B included all ports as standard; Model A required upgrades for some interfaces.

== 🔍 PCB Schematics & Service Manual ==
The BBC Micro featured a robust motherboard design, with separate logic and power supply boards in most models.

{| class="wikitable styled-table" style="width:80%; text-align:center;"
! style="background-color:#f2f2f2;"| Logic Board
! style="background-color:#f2f2f2;"| Power Supply Board
|-
| [[File:BBC_Micro_Motherboard.jpg|thumb|center|350px|BBC Micro Model B Logic Board]][[File:BBC_Micro_Schematic.png|center|thumb|BBC Micro Model B Schematic]]
| [[File:BBC_Micro_PSU.jpg|thumb|center|350px|BBC Micro Power Supply Unit]][[File:BBC_Micro_PSU_Schematic.png|center|thumb|BBC Micro PSU Schematic]]
|}

* Full service manuals and schematics are available at the [https://archive.org/details/bbc-micro-service-manual BBC Micro Service Manual (archive.org)].

== 📷 Gallery ==
<gallery mode="packed" heights="200">
File:BBC_Micro_Front_Restored.jpg|BBC Micro Model B (front view)
File:BBC_Micro_Rear.jpg|Rear panel with I/O ports
File:BBC_Micro_Keyboard.jpg|Keyboard close-up
File:BBC_Micro_Motherboard.jpg|BBC Micro Model B motherboard
File:BBC_Micro_PSU.jpg|BBC Micro power supply
</gallery>

== 🧪 Related Pages ==
* [[BBC Micro General Maintenance]]
* [[BBC Micro Troubleshooting Guide]]
* [[BBC Micro Keyboard Repair Guide]]
* [[BBC Micro Capacitor Replacement Guide]]
* [[BBC Micro ROM Upgrades]]
* [[BBC Micro Tube Expansion Guide]]

[[Category:Acorn Computers]]
[[Category:BBC Micro]]

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