The keyboard is attached to the slow bus and accessed by the system VIA. There are 74 keys including BREAK. 73 keys and 8 keyboard links are wired in a 10 × 8 matrix; the two SHIFT keys are connected to one cell and cannot be told apart. The BREAK key is on a separate circuit and resets the computer.
All keys except CTRL and SHIFT cause an interrupt when pressed, which makes the BBC scan the keyboard to identify the key(s) that are held down.
The keyboard has an unusual bit-paired layout, unlike the typewriter-paired layout that is standard on British PCs. Pressing SHIFT or CTRL neatly adds or subtracts a power of two from the ASCII value of the base character, except for the singleton characters space, 0, @, _, £ and DELETE. The layout is shown in Chapter 1 of the User Guide.
There is a circuit diagram of the keyboard on page 489 of The Advanced User Guide.
|8bs.com Type||Seen on||Key legends||Key sound||PCB colour||Chassis plate||Key switches||Space bar support||DIP switch orientation|
|Type 1||B, ?||Large||Flat||Beige||Narrow margins, lip at front||White, round body, square-edged shoulder, cross head||Plastic tabs and wire rod (concealed)||East-west (under DELETE)|
|Type 2||B, B+||Small||Echoing||Tawny brown||Wide margins, deep skirt||Black, square body, chamfered shoulder, cross head||Wire rod support||North-south|
|Type 3||?||Large||Flat||Tawny brown||Wide margins, shallow skirt||Dark grey, deep bevelled shoulder, square cup head||Plastic guides?||North-south|
|Type 4||?||Large||Echoing||Beige||Narrow margins, lip at front||Black, square body, chamfered shoulder, cross head||Wire rod support||East-west (between SHIFT and DELETE)|
-- beardo 00:01, 18 October 2007 (BST)