LCD display hardware
====================
Many applications arise when you might want to use either a cut down BBC (just
the processor, some RAM, and an IO port) in for example a burglar alarm system
or when it is not practicle to use a 14" monitor (eg.on a shop cash register).

Use of a liquid crystal display also alleviates the need for complex colour
video generating circuitry.

The system described here should work with pretty much any 20 column by 4 
line LCD based on the HD44780 controller: but check the pinout of the module
before connecting up.

PARTS...
The circuit diagram shows electrically how to assemble the unit, requiring the 
following parts:
1x  LM044L (Farnell 325-429) or PC2004AR-ASO-A (Farnell 414-6165)
1x  10k variable resistor
1x  5v power supply (eg.4xAA batteries)
1x  20 way IDC user port connector
Length of 20 way ribbon cable

BENEFITS...
*No bulky/unreliable cathode ray tubes
*Far more compact
*Runs off 5v supply
*Could be used with cut down BBCs in embedded applications
*Screen contrast adjustable for poor viewing situations

BUILD...
1.Simply split the 20 way ribbon cable and connect as suggested in the 
  diagram
2.Add the 10k potential divider to control the contrast across the marked pins
  on the diagram, be sure to get the gold card edge connectors the right way
  round
3.Add the power supply
4.Crimp the IDC plug on the other end of the ribbon cable and connect to the
  BBC micro's user port.

HINTS...
*Since LCDs are so efficient the 5v supply can be derived from the two 5v pins
 on the BBC's user port plug
*Run the software with "*LCD", it loads below the mode 7 screen memory
*The software implements all of the VDU commands which are supported by OS1.20
 and that are related to text operations. ie.You can't do any graphics 
 plotting!
*The cursor is controlled by use of VDU23 allowing it to be turned off in
 applications that require this
*The whole VDU queue is then passed on to the operating system so output will
 appear on both the LCD and the normal BBC's screen.

FROM...
Robert Sprowson.
Happy soldering!