This example circuit shows a typical application of multiplex controller/driver ICs for alphanumeric displays. The Hitachi HD44780 easily interfaces with common 4 or 8 bit microprocessors and is fully programmable for font size, duty cycle and display functions such as blinking, clearing and shifting. The character generator is capable of fixed or programmable fonts, including Japanese kana characters. By itself the HD44780 can control a display with either one or two 8-character lines.

This example is typical of Hitachi and compatible devices. See the "List of LCD Driver Chips" for information on obtaining these chips.

All LCD drive voltages are generated on-chip with the assistance of a simple resistor divider shown in detail on our page "Multiplexing LCD's". These divider networks are somewhat complicated to design, a call to our engineering department at 1-800-786-8710 may be of help during your design efforts.

The HD 44780 controller/driver supplies 16 common and 40 segment outputs. However, the display in our circuit has more than 2 lines of 5x8 dot characters, so it was necessary to expand the segment drivers to accommodate the extra characters. This was accomplished with the addition of the HD44100 which can serve as a segment driver when connected to the HD44780. The HD44780 supplies all of the timing and power necessary for operation, making expansion very straightforward. Up to nine HD44100 can be added to the circuit, however the internal RAM supports a maximum of 80 display characters total.

The software to make this chip work is not difficult, however it is beyond the scope of this document. An explanation of the internal workings of the chip, and the programming necessary to make it work are found in the LCD CONTROLLER / DRIVER LSI DATA BOOK available from Hitachi. See the "List of LCD Driver Chips" for information on contacting them. This data book also contains all of the waveforms typical of this circuit.