Hitachi HD44780 LCD controller

The integrated circuit Hitachi HD44780 is the de facto industry standard control unit for small alphanumeric dot matrix LCD modules. This assumes the appearance of text by an integrated character generator ROM and takes care of the complete drive including the creation of all the necessary signals for the display. The original Hitachi HD44780 is now no longer manufactured, but there are numerous replicas usually fully compatible and compatible LCD controllers, such as Sunplus SPLC780A1, Sitronix ST7066 and Samsung KS0066.

LCD display modules according to standard HD44780

In ancient LCD modules of HD44780 as Thin Quad Flat Package module ( TQFP- block) was soldered in new LCD modules are almost exclusively to find replicas of the HD44780 that are bonded directly to the board (COB ) technique. Such display modules are available in configurations 8 × 1 character to 40 × 4 characters available and contain the HD44780 and if necessary the column driver HD44100 already integrated on the module. The display module is thus already assembled, ready for use in microcontroller circuits and microprocessor bus systems. HD44780 -compatible LCD modules now exist in almost every imaginable color combinations of the backlight and polarization and have fallen rapidly in price, thus, for example, a backlit display module with 16 x 2 characters already available under 7 euros.


Due to the low price, the good availability of many manufacturers and the light control you find these display modules in many copiers, fax machines, laser printers, network devices (such as routers, switches, servers) as well as in measurement and industrial devices for operator guidance and output of status information. HD44780 - compatible LCD modules are also popular with electronics hobbyists in conjunction with microcontrollers and the PC modding scene for displaying system information (eg, CPU load ) on the LPT port.

Such display modules are usually not used in consumer electronics devices such as VCRs or DVD players, since the use of vendor-specific -made application-specific displays is here cheaper or more effective. A HD44780 -compatible LCD module is more of a generic solution that is intended for a broad range of applications.

Connection to microcontroller

The communication with the microcontroller is carried out in parallel in the 4-bit mode or 8- bit mode. Even with 8-bit microcontroller, the 4- bit control is often preferred since these four I / O lines needs less.

In 4-bit control, the transmission of the data in two halves in a row sent (nibbles ) is carried.

The electrical connection is not standardized, but there is a de facto standard to which hold most manufacturers. It is advisable, however, to consult before starting up a display module, the data sheet, as in some modules, the cables for the power supply (VSS and VDD) are reversed, and some very rare specimens differ from the quasi-standard. Incorrect connection of the power supply may lead to the immediate destruction of the module.

Font and character set

The internal CGROM ( character generator ROM ) contains 208 characters in a 5 x 8 array and 32 x 10 characters in a 5 - matrix, the latter is, however, used in almost any LCD module. In addition, a CGRAM exists ( a character generator RAM ) can be used in which 8 user-defined characters in a 5x8 matrix or 4 characters uploaded in a 5x10 matrix. Thus, graphics, umlauts, Cyrillic or bar graphs can for example be displayed on such modules, which are not included in the internal CG ROM these symbols.

The most common standard character set ( HD44780A00 ) contains an almost complete ASCII character set (without backslash and tilde ), and Japanese katakana symbols and some symbols. Other character sets contain Cyrillic characters or umlauts ( HD44780A02 ) instead of katakana characters. Partial soft some Cyrillic fonts today replicas depending on the manufacturer of each other, since there was no submission on the part of Hitachi HD44780 here.