|
Unlike the venerable HD44780 based character LCD, graphic LCDs do not have any ad-hoc standard. Small graphic LCDs come in many different flavors, configurations and sizes. Some have on-board dedicated graphic controller chips and some do not. All graphic LCDs require a negative voltage to drive the displays contrast. The amount varies with the physical size of the display. Usually, 240x64, and less, require -10v, 256x128 need -15v and larger displays may require up to -24v. To further complicate matters, this required negative voltage is usually not provided by the LCD itself. This means additional circuitry. To drive an LCD without an on-board graphic controller with an 8 bit micro would be daunting, indeed, and is beyond the scope of the Workbench boards. All of the COMPSys Workbench development boards rely on LCDs with controllers. This usually requires 12-16 pins of the micro, and leaves the rest of the micro’s pins for the user to implement for other uses such as I/O, analog readings, buttons, keypads etc. Some graphic LCDs even have a serial interface requiring only a handful of connections. Three of the popular controllers for small size displays are the Seiko-Epson SED1330, Samsung KS0108 (akin to the Hitachi HD61202), and the Toshiba T6963C. Most of the LCDs that use these controllers have an 8 bit data bus along with 4 to 6 control lines. The Workbench controllers are configured to work with most of the above controllers. Since pin arrangements vary from one manufacturer to another, adapters become a necessity. All of the LCDs mentioned here a 1 bit color displays (black/white) and are not capable of grayscale shades.
|
