BeebEm - BBC Micro and Master Series Emulator

Keyboard Links

The BBC Model B (and B+) features a set of eight links as part of the keyboard interface. These links control certain behaviours of the OS or DFS, described in the Advanced User Guide, page 274.

BeebEm Keyboard Links dialog box

Default filing system

Bit 7 selects the default filing system, either NFS (when set) or DFS (when clear).

Disc drive timing

Bit 5 and bit 4 control disc drive timings, depending on the type of floppy disc controller. BeebEm currently ignores these settings.

Bit 5 Bit 4 8271 Timings 1770 Timings 1772 Timings
0 0 Step: 24 ms, settle: 20 ms, head load: 64 ms Step: 30 ms, settle: 30 ms Step: 3 ms, settle: 15 ms
0 1 Step: 6 ms, settle: 50 ms, head load: 32 ms Step: 20 ms, settle: 30 ms Step: 2 ms, settle: 15 ms
1 0 Step: 6 ms, settle: 16 ms, head load: 0 ms Step: 12 ms, settle: 30 ms Step: 12 ms, settle: 15 ms
1 1 Step: 4 ms, settle: 16 ms, head load: 0 ms Step: 6 ms, settle: 30 ms Step: 6 ms, settle: 15 ms

Reverse Shift + Break action

Bit 3 reverses the action taken on Shift + Break, i.e., if this bit is set (ticked), pressing Break will cause DFS to boot from floppy disc.

Screen mode

Bits 0 to 2 select the default screen mode enabled on start up. Set these bits as shown below to select a given screen mode.

Bit 2 Bit 1 Bit 0 Description
0 0 0 Mode 7
0 0 1 Mode 6
0 1 0 Mode 5
0 1 1 Mode 4
1 0 0 Mode 3
1 0 1 Mode 2
1 1 0 Mode 1
1 1 1 Mode 0