PS/2 keyboard port
==================
In some applications it is preferable to 'hide' the controlling BBC micro
away, for example in a rack unit or in the ceiling void, and simply present
a keyboard terminal interface for the occasions where user interaction is
needed.

The only minor problem with this approach is that the keyboard interface on
the BBC micro is a very specific parallel interface where one of the system
VIA ports scans the matrix manually over a short parallel link - this doesn't
lend itself to being extended over long distances nor is the BBC micro 
keyboard a standard shape for boxes: the PS/2 keyboard port project allows
you to connect a cheap PC keyboard to your machine.

This would conversely allow you to put the BBC micro motherboard into a PC case
for example.

PARTS...
The circuit diagram shows electrically how to assemble the unit, requiring the 
following parts:
2x  BC182 NPN transistors
2x  10k resistors
2x  1.6k resistors
1x  6 pin mini DIN PS/2 socket
1x  20 way IDC user port plug and a short piece of ribbon cable

In addition, it may be useful to have a couple of pins for clipping an
oscilloscope or logic probe to.

BENEFITS...
*Use low cost PC keyboards and PC keyboard/monitor switches
*Gain a numeric keypad even on the BBC model B
*Works with any 'type 2' keyboard
*Ignores unrecognised key strokes such as the 'Windows keys'
*Simple interface circuit can be fitted internally to the microcomputer
*Driver supports all the usual key scanning OS calls

BUILD...
1.Crimp the short length of ribbon cable to the 20 way IDC connector for the
  user port.
2.Splay out the lines for CB1, PB0, PB1, PB2 and their corresponding ground 
  wires.
3.Wire up the two transistors and four resistors per the circuit diagram on
  a small offcut of prototyping board and solder on the 4 signal lines.
4.Secure the ribbon cable with a blob of hot glue and fit the DIN connector.
5.Plug the adapter into the user port and power up the PS/2 keyboard, then
  simply run the supplied driver and start typing.

HINTS...
*Pretty much any small NPN transistor will do, they're only being used to 
 provide open collector outputs from the BBC micro's output-only user port.
*Most keyboards can be run in several modes, the software driver switches it to
 'type 2' every time it is run so the choice of keyboard should be pretty
 unrestricted - even wireless ones!
*The software is assembled to run below the MODE 7 screen memory at &7500
 and also features in MiniB (the floppy disc sized BBC micro from the same
 author).

FROM...
Robert Sprowson.
Happy soldering!