Editing Acorn BBC Microcomputer

{{infobox dkeyboard
| name         = BBC Microcomputer keyboard
| image name   = Acorn BBC Microcomputer.jpg
| pn           = 
| fcc          = 
| branding     = [[BBC]]
| manufacturer = [[Wong's]], [[SMK]], [[PED]]
| features     = 
| switch       = [[Futaba MR-6C series]]<br>[[SMK J-M0404 series]]<br>[[PED keyswitch]]
| layouts      = 
| interface    = Proprietary internal
| weight       = 
| years        = 
| switch mount = [[Plate mount]]
| keycaps      = [[Double-shot]] [[spherical keycap|spherical]]
}}

The '''BBC Microcomputer System''' from [[Acorn|Acorn Computers Ltd]], commonly known as the '''BBC Micro''' or '''Beeb''', was a series of 6502-based 8-bit microcomputers introduced in the United Kingdom in late 1981/early 1982.

==Overview==
Unusually for an 8-bit home computer, these computers used discrete mechanical switches, mounted in aluminium and steel plates. Switches were sourced from [[Futaba]], [[PED]] and [[SMK]]. The three different brands of switch used different [[keycap mount]]s and the keycaps are not interchangeable between keyboard types, except presumably the two SMK types.

All the variants were supplied with [[spherical keycap|spherical]] [[double-shot molding|double-shot]] keycaps in a curious combination of black (technically very dark brown), flame red for the [[function keys]], and olive drab for the [[cursor keys]]. The differences between the variants are minor.

The keyboard is integrated into the computer; it is secured by two screws and nuts and is extremely easy to remove, after removing the four screws that retain the case lid. Unusually for a plate-mounted keyboard, it is the PCB and not the mounting plate that is screwed down. The keyboard has two cables that connect to the motherboard: one ribbon cable for the matrix, and the speaker cable, as the speaker is integrated into the keyboard. The keyboard also has capacity for fitting a ROM socket, usually used for speech synthesiser ROMs, and a [[DIP switch]] bank for setting hardware configuration.

<gallery widths="250" heights="187">
File:Straight outta Comptec.jpg|Type 3, 4 and 1 keycaps and switches; these types all used Comptec keycaps
</gallery>

===Operation===
Unlike a protocol such as the [[AT keyboard interface]], the BBC Micro keyboard does not transmit keypresses as they occur. All the matrix rows are connected at one end to a 74LS30 NAND gate,<ref name="AUG-489-90" /> which is in turn connected to CA2 (port A control line 2) of the System VIA; this control line generates the keyboard interrupt. (The VIA chips are MOS 6522 Versatile Interface Adapter ICs found on the computer motherboard.) The matrix columns are strobed continually at 1 MHz; when any key is pressed, the OS receives the interrupt signal, and takes control of the keyboard scanning. During controlled scanning, the matrix rows are sensed individually to identify which keys are pressed.<ref name="Arduino" /> Detection of key ''release'' however is unexplained.

Acorn MOS supports two-key rollover; two locations in zero page (&EC and &ED) hold the non-modifier keys currently depressed, or zero otherwise.<ref name="AUG-142" />  Row zero of the matrix has anti-ghosting diodes fitted<ref name="AUG-489-90" /> which allows contacts in this row to be detected simultaneously with any two keys elsewhere in the matrix.  Row zero contains the modifier keys '''shift''' and '''control''' and the start-up options.

===Start up options===
The BBC Micro has no writable, non-volatile memory. To partially alleviate this, eight bits of "start up options" can be set in hardware. These options control the default screen mode (bits 0–2, switches 6–8), reversal of shift+break (bit 3, switch 5), and diskette drive parameters (bits 4 and 5, switches 3 and 4); bit 6, switch 2, is not used.<ref name="AUG-489-90" /><ref name="8bs" />  In a machine fitted with the DNFS filing system ROM bit 7, switch 1, is used to control the default filing system should both disc and network hardware be fitted, otherwise it is not used.<ref name="DNFS" /> These eight bits occupy columns two through nine of the first row of the keyboard matrix and function as keys.

Solder pads are provided on the keyboard PCB to affix a DIP switch block; alternatively the settings can be hard-wired using links. By default, each of these eight bits defaults to zero.

==Keyboard types==
Prior to the identification of the switches, the keyboards were classified by Chris Richardson of 8-Bit Software into four types,<ref name="8bs" /> which are not numbered in the order that they were introduced. These type numbers are used here for convenience.

===Type 1===
This is the original and most common keyboard type, with an aluminium plate and [[Futaba MR-6C series]] switches. This appears to have been manufactured from the 1981 to 1984. The OEM was [[Wong's]]. The keycaps were manufactured by [[Comptec]]; this is not only evident from the design, but [[Signature Plastics]] have confirmed that Wong's was a major customer.<ref name="SP" /> "Keytop set 'Comtec'" {{sq|sic}} (£20.83) and "Spacebar (Comtec)" (£0.66) are listed in a catalogue, but the specific keyboard for which it was intended is not given.<ref name="MDFS" />

<gallery widths="250" heights="187">
File:BBC Micro keyboard.jpg                                | Issue 4 model B with Type 1 keyboard
File:BBC Micro spherical double-shots.jpg                  | Spherical keycaps from a Type 1 keyboard
File:BBC Micro Type 1 switches.jpg                         | Type 1 with its Futaba switches; you can see where the keyboard's PCB is secured to the case
File:BBC Micro Type 1 switches mounted.jpg                 | Type 1 keyboard from the side
File:BBC Micro Type 1.jpg                                  | Type 1 keyboard: the keycaps are in fact very dark brown
File:BBC Micro Type 1 -- PCB.jpg                           | PCB viewed from below
File:BBC Micro Type 1 -- Acorn branding.jpg                | Branding
File:BBC Micro Type 1 -- connectors.jpg                    | Speaker and data connectors
File:BBC Micro Type 1 -- DIP switch holes, top.jpg         | DIP switch mounting holes for start up options
File:BBC Micro Type 1 -- DIP switch holes, bottom.jpg      | DIP switch mounting pads
File:BBC Micro Type 1 -- Futaba stabiliser mount.jpg       | Futaba stabiliser mount
File:BBC Micro Type 1 -- LEDs.jpg                          | LEDs
File:BBC Micro Type 1 -- plate-mounted Futaba switches.jpg | Plate-mounted switches
File:BBC Micro Type 1 -- speaker.jpg                       | Speaker and speaker grille
</gallery>

===Type 1a===
This very similar to, and is believed to be a precursor to, the type 1.  It does not have the speaker grille and the placement of some components is slighly different.  The assumption is that components were moved between this and the type 1 to introduce the speaker grille.

<gallery widths="250" heights="187">
File:BBC_Micro_KB_Type1a_Speaker.jpg                       | Type 1a speaker without grille.
File:BBC Micro Keyboard Type 1a Front View.jpg             | Type 1a Front View
File:BBC Micro Keyboard Type 1a Top View.jpg               | Type 1a Top View
File:BBC Micro Keyboard Type 1a Back View.jpg              | Type 1a Bottom (PCB) View.
</gallery>

===Type 2===
[[SMK J-M0404 series]] switches with angled keystems, mounted onto a steel plate. Known manufacturing dates are from 1984. The OEM was [[SMK]], part number 401KBM-006-90RⒶ. The shift keys, space bar and possibly also tab use the brown and beige low-friction version of the switch.<ref name="8bs" /> These switches have been reported to be unreliable.<ref name="8bs" /> The keycaps were sourced from SMK, as they fit SMK's moulding style.

The return key uses a pair of low-force switches in tandem, connected together on the PCB.<ref name="Correspondence" /> These switches have the brown slider indicative of low friction switches, together with a beige base.

<gallery widths="250" heights="187">
File:BBC Micro SMK keyboard -- switches and keycap.jpg | Standard switches and keycap
File:SMK vintage linear, low friction variants.jpg     | Low friction switches: standard weight (left) and low force (right)
</gallery>

===Type 3===
[[PED keyswitch]]es.<ref name="MDFS" /> The mounting plate is aluminium. Also known to be manufactured in 1984. The PCB is not branded. The keycaps were supplied by Comptec.

<gallery widths="250" heights="167">
File:BBC Micro Type 3.jpg                              |Top view
File:BBC Micro Type 3 -- front view.jpg                |Bottom view
</gallery>

===Type 4===
[[SMK J-M0404 series]] switches with upright keystems, on an aluminium plate. Also known to be manufactured in 1984. The OEM was [[Wong's]]. The keycaps were supplied by Comptec.

==Later computers==
The Acorn Electron and the original Master Series machines used [[Futaba low-profile linear]] switches. The Master Compact used conductive [[rubber dome]]s over a PCB, and later Master 128s used [[Cherry MY]] switches.<ref name="8bs" /> The Futaba low-profile linear switch did not have anything close to the reliability level of the simplified linear model.

==External links==
*wouter.bbcmicro.net — [https://web.archive.org/web/20150420214735/http://wouter.bbcmicro.net/pictures/computer/keyboard/index.html Pictures of BBCs] (Wayback Machine)
*wouter.bbcmicro.net — [https://web.archive.org/web/20170305231341/http://wouter.bbcmicro.net/bbc/serial_numbers.html BBC serial numbers and dates] (Wayback Machine)

==References==
<references>
<ref name="DNFS">Acorn Computers Ltd — [http://chrisacorns.computinghistory.org.uk/docs/Acorn/Tech/Acorn_TheDNFS-ib.pdf ''The DNFS instruction booklet'', chapter 4, page 9] (Chris's Acorns / The Centre for Computing History)</ref>
<ref name="8bs">8-Bit Software — [http://8bs.com/insides.htm See Their Insides]</ref>
<ref name="MDFS">BBC Micro Mailing List — [http://mdfs.net/Archive/BBCMicro/2005/09/14/012246.htm Subject: Interesting DRAM catalogue]</ref>
<ref name="SP">Correspondence with Signature Plastics, 2015-10-02</ref>
<ref name="AUG-489-90">Bray, Andrew C; Dickens, Adrian C; Holmes, Mark A — ''The Advanced User Guide for the BBC Microcomputer'' — pp. 489–90: Appendix J — The keyboard circuit</ref>
<ref name="AUG-142">Bray, Andrew C; Dickens, Adrian C; Holmes, Mark A — ''The Advanced User Guide for the BBC Microcomputer'' — p. 142: OSBYTE &78 (120) *FX 120</ref>
<ref name="Arduino">Arduino Forum — [http://forum.arduino.cc/index.php?topic=62962.0 BBC Micro Keyboard]</ref>
<ref name="Correspondence">Correspondence with Andrew from CJE Micro's, 2016-10-06</ref>
</references>

[[Category:Computers]]
[[Category:Integrated keyboards]]
[[Category:Acorn keyboards]]
[[Category:SMK OEM keyboards]]
[[Category:Wong's OEM keyboards]]
[[Category:Keyboards with SMK J-M0404 switches]]
[[Category:Keyboards with Futaba MR switches]]