HD44780
The Hitachi HD44780 integrated circuit is the de facto industry standard control unit for small alphanumeric dot matrix LCD modules. It takes over the representation of text through an integrated character generator ROM and takes care of the complete control including the generation of all necessary signals for the display . The original Hitachi HD44780 is no longer manufactured, but there are numerous mostly fully compatible replicas and LCD control units, such as Sunplus SPLC780A1, Sitronix ST7066 or Samsung KS0066.
LCD display modules according to the HD44780 standard
In old LCD modules, the HD44780 was soldered as a Thin Quad Flat Package (TQFP) component, while new LCD modules almost exclusively contain replicas of the HD44780, which are bonded directly to the circuit board ( COB technology ). Such display modules are available in the configurations 8 × 1 characters to 40 × 4 characters and contain the HD44780 and, if necessary, the column driver HD44100 already integrated on the module. The display module is therefore ready for connection for use in microcontroller circuits and microprocessor bus systems. HD44780-compatible LCD modules exist today in almost every imaginable color combination of backlighting and polarization and have fallen rapidly in price, for example a backlit display module with 16 × 2 characters is available for less than 7 euros.
use
Due to the low price, the good availability from many manufacturers and the easy control, these display modules can be found in many copiers, fax machines, laser printers, network devices (e.g. routers, switches, servers) as well as in measuring and industrial devices for operator guidance and output of status information. HD44780-compatible LCD modules are also popular with electronics hobbyists in connection with microcontrollers and in the PC modding scene for outputting system information (for example processor load) via the LPT connection .
HD44780 compatible LCD modules serve as a generic solution for a wide range of applications.
In mass products such as video recorders, tuners / hi-fi amplifiers or DVD players, on the other hand, manufacturer-specific, application-specific displays (LCD or fluorescent display ) that contain special symbols or graphics are often used.
Connection to microcontroller
Communication with the microcontroller takes place in parallel in 4-bit or 8-bit mode. With 8-bit microcontrollers, too, 4-bit control is often preferred because it requires fewer four I / O lines.
| symbol | Art | description |
|---|---|---|
| Vss | Dimensions | GND (ground reference) |
| RS | I. | 0 = command, 1 = data |
| R / W | I. | 0 = write, 1 = read |
| E. | I. | Enable |
| D4 | I / O | Data bit 0 (LSB) |
| D5 | I / O | Data bit 1 |
| D6 | I / O | Data bit 2 |
| D7 | I / O | Data bit 3 (MSB) |
| symbol | Art | description |
|---|---|---|
| Vss | Dimensions | GND (ground reference) |
| RS | I. | 0 = command, 1 = data |
| R / W | I. | 0 = write, 1 = read |
| E. | I. | Enable |
| D0 | I / O | Data bit 0 (LSB) |
| D1 | I / O | Data bit 1 |
| D2 | I / O | Data bit 2 |
| D3 | I / O | Data bit 3 |
| D4 | I / O | Data bit 4 |
| D5 | I / O | Data bit 5 |
| D6 | I / O | Data bit 6 |
| D7 | I / O | Data bit 7 (MSB) |
- ↑ a b I = input (input line), O = output (output line)
- ↑ a b if not read or the busy flag has to be queried, this line can also be set to 0.
With 4-bit control, the data is transmitted in two halves (nibbles) sent one after the other.
The electrical connection is not standardized, but there is a quasi-standard that most manufacturers adhere to. However, it is advisable to consult the data sheet before commissioning a display module, as the cables for the power supply (VSS and VDD) are interchanged on some modules, and some rare copies deviate entirely from the quasi-standard. An incorrect connection of the power supply can lead to the immediate destruction of the module.
| Pin no. | symbol | Art | function |
|---|---|---|---|
| 1 | VSS | Power supply | GND (ground) |
| 2 | VCC | Power supply | + 5V |
| 3 | VEE | Power supply | Contrast tension |
| 4th | RS | Data line | 0 = command, 1 = data |
| 5 | R / W | Data line | 0 = write, 1 = read |
| 6th | E. | Data line | Enable |
| 7th | D0 | Data line | Data line 0 |
| 8th | D1 | Data line | Data line 1 |
| 9 | D2 | Data line | Data line 2 |
| 10 | D3 | Data line | Data line 3 |
| 11 | D4 | Data line | Data line 4 |
| 12 | D5 | Data line | Data line 5 |
| 13 | D6 | Data line | Data line 6 |
| 14th | D7 | Data line | Data line 7 |
| 15th | A. | Power supply | Backlight anode (+) |
| 16 | K | Power supply | Backlight cathode (-) |
- ↑ a b If there is a backlight. With some modules 5 V must be applied, with others the current has to be limited by a series resistor .
Font and character set
The internal CGROM (character generator ROM) contains 208 characters in a 5 × 8 matrix, as well as 32 characters in a 5 × 10 matrix, the latter, however, is hardly used in any LCD module. In addition, there is a CGRAM (a character generator RAM) in which 8 user-defined characters in a 5 × 8 matrix or 4 characters in a 5 × 10 matrix can be uploaded. Thus, for example, graphics, umlauts, Cyrillic characters or bar graphics can be displayed on modules that do not contain these symbols in the internal CGROM.
The most common standard character set (HD44780A00) contains an almost complete ASCII character set (without backslash and tilde) as well as Japanese katakana symbols and a few other symbols. Other character sets contain Cyrillic characters or umlauts instead of the katakana characters (HD44780A02). Some of the Cyrillic character sets of today's replicas differ from one another depending on the manufacturer, as there was no template from Hitachi's HD44780.
Web links
- Hitachi HD44780U (LCD-II) data sheet (PDF-File; 322 kB)
- Sprut.de Dot-Matrix LC-Displays General information on display commands and memory organization (not PIC-specific)
- Custom character on the LCD