lcd displays that are compatible with the hitachi hd44780 driver made in china

The closest thing to a standard is, unfortunately, for LCD panels that have controllers but no drivers. IIRC, a typical interface will have signals for phase polarity, frame clock, line clock, data clock and 4 data bits. Every line of pixels one should clock in enough groups of four pixels to fill the width of the display (extra bits will be ignored), driving the data clock high and low for each group. The drive the line clock high and low to strobe the line. The first line of each frame should have the frame clock high, and the phase polarity signal should toggle every frame.

The line clock signals, and those derived from them, must be sent at a uniform rate. The precise timing of the data clock signals, however, doesn"t matter provided that all the clocks happen for a line happen within the proper window. If you don"t have DMA, it may be possible to keep a small display happy and still have time to do something else, but refreshing the display will be a pain. If you do have DMA, however, and can manage a small CPLD to handle a few aspects of the timing, implementing the display that way may be very rewarding. I"ve done a display panel like that and achieved display-update performance superior to anything I could have done with a conventional display controller. I even achieved 4-level gray-scale by running the display at 100 frames/second and, every three frames, driving the display twice using one buffer and once with another.

The Hitachi HD44780 LCD controller is an alphanumeric dot matrix liquid crystal display (LCD) controller developed by Hitachi in the 1980s. The character set of the controller includes ASCII characters, Japanese Kana characters, and some symbols in two 40 character lines. Using an extension driver, the device can display up to 80 characters.

The Hitachi HD44780 LCD controller is limited to monochrome text displays and is often used in copiers, fax machines, laser printers, industrial test equipment, and networking equipment, such as routers and storage devices.

Compatible LCD screens are manufactured in several standard configurations. Common sizes are one row of eight characters (8×1), and 16×2, 20×2 and 20×4 formats. Larger custom sizes are made with 32, 40 and 80 characters and with 1, 2, 4 or 8 lines. The most commonly manufactured larger configuration is 40×4 characters, which requires two individually addressable HD44780 controllers with expansion chips as a single HD44780 chip can only address up to 80 characters.

Character LCDs may have a backlight, which may be LED, fluorescent, or electroluminescent. The nominal operating voltage for LED backlights is 5V at full brightness, with dimming at lower voltages dependent on the details such as LED color. Non-LED backlights often require higher voltages.

Character LCDs use a 16-contact interface, commonly using pins or card edge connections on 0.1 inch (2.54 mm) centers. Those without backlights may have only 14 pins, omitting the two pins powering the light. This interface was designed to be easily hooked up to the Intel MCS-51 XRAM interface, using only two address pins, which allowed displaying text on LCD using simple MOVX commands, offering cost effective option for adding text display to devices.

Vee (also V0): This is an analog input, typically connected to a potentiometer. The user must be able to control this voltage independent of all other adjustments, in order to optimise visibility of the display that varies i. a. with temperature and, in some cases, height above the sea level. With a wrong adjustment, the display will seem to malfunction.

R/W: In most applications, reading from the HD44780 is not necessary. In that case, this pin can be permanently connected to ground and no processor pins need to be allocated to control it.

In 8-bit mode, all transfers happen in one cycle of the enable pin (E) with all 8 bits on the data bus and the RS and R/W pins stable. In 4-bit mode, data are transferred as pairs of 4-bit "nibbles" on the upper data pins, D7–D4, with two enable pulses and the RS and R/W pins stable. The four most significant bits (7–4) must be written first, followed by the four least significant bits (3–0). The high/low sequence must be completed each time or the controller will not properly receive further commands.

Selecting 4-bit or 8-bit mode requires careful selection of commands. There are two primary considerations. First, with D3–D0 unconnected, these lines will always appear high (binary 1111) to the HD44780 since there are internal pull-up MOSFETs.

The same command is sent three times, Function Set with 8-bit interface D7–D4 = binary 0011, the lower four bits are "don"t care", using single enable pulses. If the controller is in 4-bit mode, the lower four bits are ignored so they cannot be sent until the interface is in a known size configuration.

In all three starting cases, the bus interface is now in 8-bit mode, 1 line, 5×8 characters. If a different configuration 8-bit mode is desired, an 8-bit bus Function Set command should be sent to set the full parameters. If 4-bit mode is desired, binary 0010 should be sent on D7–D4 with a single enable pulse. Now the controller will be in 4-bit mode and a full 4-bit bus Function Set command sequence (two enables with command bits 7–4 and 3–0 on subsequent cycles) will complete the configuration of the Function Set register.

The CGRAM is read/write memory used to encode up to 8 characters in the character generator. It consists of 64 fields at addresses 0 to 3F hex. Each field is 5 bits mapping to a row of pixels of each character. Each 8 fields in the CGRAM are used for each character. The lower 3 bits of the character codes from 0–7 and 8–15 select the groups of 8 fields in the CGRAM memory.

Reading and writing to the DDRAM is done by setting the RS input high during bus transfers. The DDRAM must also be selected by using the Set DDRAM address command which selects the DDRAM for access and also sets the starting address for DDRAM access.

Likewise reading and writing to the CGRAM is done by setting the RS input high during bus transfers. The CGRAM must also be selected by the Set CGRAM address command which selects the CGRAM for access and also sets the starting address for CGRAM access.

The execution times listed in this table are based on an oscillator frequency of 270 kHz. The data sheet indicates that for a resistor of 91 kΩ at VCC=5 V the oscillator can vary between 190 kHz and 350 kHz resulting in wait times of 52.6 µs and 28.6 µs instead of 37 µs. If a display with the recommended 91 kΩ resistor is powered from 3.3 volts the oscillator will run much slower. If the busy bit is not used and instructions are timed by the external circuitry, this should be taken into account.

The original HD44780 character generator ROM contains 208 characters in a 5×8 dot matrix, and 32 characters in a 5×10 dot matrix. More recent compatible chips are available with higher resolution, matched to displays with more pixels.

The 7-bit ASCII subset for the Japanese version is non-standard: it supplies a Yen symbol where the backslash character is normally found, and left and right arrow symbols in place of tilde and the rubout character.

A limited number of custom characters can be programmed into the device in the form of a bitmap using special commands. These characters have to be written to the device each time it is switched on, as they are stored in volatile memory.

Huang, Han-Way (2009). The HCS12 / 9S12: An Introduction to Software and Hardware Interfacing (2nd ed.). Delmar Cengage Learning. ISBN 978-1-4354-2742-6.

CFAG19232C-TMI-TT Rev.014 should work as a drop in replacement for the CFAG19232C-TMI-TT Rev.011. The only changes to the module effected the LCD bias circuit. Since the module is shipped with fixed (controlled by ST7920) contrast, we do not anticipate any issues migrating to the new revision.

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Apparently you did it right -> putting your code in these characters does exactly what we see now -> your code in a separate window, selectable and scrollable. Good job for first time poster!

means, that your LCD has to be connected accordingly to the pins, which are assigned by the constructor as ... lcd (rs, enable, d4, d5, d6, d7) and thus only works when you have wired your display as follows:

You can also use other pins of your MEGA, but then you have to adjust the pin assignment in the constructor as described above; the only condition is, that the constructor"s pin assignment corresponds to your wiring.

So pls check again, if all of your wiring is EXACTLY as I listed here (identical with the instructions in your example sketch). Even if so - a common issue for beginners with LCD displays is, to have no solid connections between Arduino and LCD display.

We had newbies here which didn"t solder the wires at all, just bent them around the pcb hole -> this is a no go and will never work! Also: "cold" solder spots are no good idea. Your connections have to be solid, anything else will fail or cause trouble.

And: when you had to make modification(s), use the potentiometer again as it might work after your modification, but the contrast of the display is not set right.

Character based LCD displays are great: they are inexpensive, and it is rather simple to use them compared to graphical displays. Yes, they only can display text and custom symbols, but this is usually what I need. And pretty much all character displays are using the Hitachi HD44780 protocol, so it is a de-facto industry standard.

These displays have one big disadvantage: they need to be compatible with the original Hitachi interface and protocol. First display were mostly one line only, and had only few characters, typically up to 16. The protocol worked either with one or two lines on the display. Today’s display have usually two lines, with 16 characters. But what if I need more?

These HD44780 displays can run in 4bit or 8bit mode, and in the smallest configuration (4bit mode) the connection to the microcontroller only needs 6 wires:

The original protocol had a big problem: there is no handshaking between microcontroller and display. If the microcontroller writes to the display, it needs to wait until the display has finished the operation until a new write operation can start. So the micrcontroller needs to wait some time, depending on the display speed. To overcome this problem, later displays had added the R/W (Read/Write) signal which allows the microcontroller to read the status from the display (if the display is ready to accept new data). So if you consider to use a display, make sure it has that R/W line implemented.

So writing at address 0x00 would be the first character on line 1, 0x01 the second, and so on. Writing at address 0x40 would be the first character on the second line, and so on. That would allow up to 64 characters per line. A 16-character display would show the characters e.g. from address 0x00-0x0F. The other bytes in the address map could be used to ‘scroll’ the text to the right/left using special display commands:

As this feature has not been used much, and there was a bigger customer needs for having 4 lines of text, some vendors decided to change the memory map to support 4 lines (see “Character LCD with 4 Lines”):

If I want now to have 4 lines with more than 16 characters, something different is needed. My display driver (LCDHTA, see “HD44780 2×16 Character Display for Kinetis and Freedom Board“) worked fine, but not for a 4×40 display which was used by a reader of this blog :-(: the NewHaven NHD-0440WH-ATFH-JT Display:

Until I realized: they have put 2 display controller together! This display is not really a 4×40 character display, it is two 2×40 displays in a single display packaging :-). This is the same as if I would combine two displays on the same bus like this:

As I did not had the Newhaven 4×40 display available to verify the driver, I wired two 2×16 displays together. And with this, I was able to build a 4×16 (potentially 4×64) character display:

The Hitachi HD44780 is very common and can be considered as ‘industry standard’. But as with any standards, it comes with limitations, and standards sometimes make it hard to move the technology to the next level. And sometimes it causes kind of strange solutions as creating a 4 line display with two display controllers on it. Switching the Ex lines I can now support up to for 4 lines and up to 64 characters for each line. And if needed, I can extend that concept for more lines/displays.

Now that we have access to the I²C GPIO expander, we yet have to find out which GPIO on the expander is wired to which pin of the screen. We will have to provide this information into the device tree, as it is explained in the hit,hd44780.txt file in the kernel documentation.

I will copy it here, as it is short enough, and also because unused drivers and their documentation have the tendency to disappear in the kernel — and I fear that this driver may one day be removed because so many users prefer to use some userspace Python code or stuff to talk to this kind of device.

So, we need to add this auxdisplay node in our device tree, and configure it with the pins of the PCF8574A (remember, we declared it as a gpio-controller just before).

For this, one could go with a multimeter to probe between the expander and the screen"s pins to understand how it was designed. But this screen setup is so cheap and familiar in the maker community that the LiquidCrystalI2C Arduino library will be a great candidate for retro engineering out the pinout.

By digging into the code — which is not easy to the eyes after passing so much time reading the Linux driver code — we can identify the few defines that identify the screen"s pins by numbers that are the number of the GPIO pin of the expander.

We can see that the bits used for the data are the 4..7 bits, because the values highnib and lownib are bitwise-and masked with 0xf0 — which represent the top most 4 bits of a byte. This way, we can establish the following layout of the GPIO expander to the screen from our retro engineering of the library:Pin number (GPIO expander)76543210

We can then add the screen to the root of the SBC"s device tree — because there is no reason to put it under the GPIO expander — and then configure the screen entry to use the expander"s pins [1].

After a try when the screen was displaying some stuff but the backlight was always off (so almost illegible on the white/blue screen variant), I had to change the backlight-gpios node to use GPIO_ACTIVE_LOW in order for the backlight to illuminate the screen at boot.

Sending a "backlight on" command to the screen turned the backlight off, so this step was an error. Indeed, the driver wants to activate the backlight only when necessary, but for me I like when it is always on, so I let this as-is even if it is not correct. The correct solution would be to enable the backlight on at the startup and keep it always on (or think to blink it when you put a message, the driver supports that too).

I was previously using an Arduino pro mini and had my project working flawlessly. I wanted to introduce some RF communication capabilities so I picked up some Moteinos. I am using the Moteino Mega with my 16x2 LCD display:

I understand that the Moteino products run on 3.3V and that LCD shield runs on 5V. I am correctly powering the LCD shield with 5V and I am using Moteino Mega digital pins 16 through 22 (I don"t see any conflict with the pins used for the RFM69) connected to a Nexperia 74LVC4245A translator to shift from 3.3V to 5V for the LCD pins.

My first test was to upload the program I was previously using with my Pro Mini to the Moteino Mega just to make sure the LCD screen / buttons, etc were working. Of course in my program I had to change the pin numbers to the appropriate pin numbers on the Moteino Mega, but nothing else was altered. Unfortunately, the LCD screen shows nothing on the screen.

I"ve checked over the connections 100 times now, verified the pin numbers are correct, verified that the translator is working correctly (I connected each of the pins to 3.3V to make sure the corresponding output one reliably outputs 5V). I cannot seem to get the LCD screen to print anything. I then used the very simple "Hello World" example program and still nothing. I also plugged my LCD screen back into my pro mini project board and it works flawlessly. No problems with the LCD screen being fried.

I am thinking that something in the LiquidCrystal library is not playing nicely with the Moteino MEGA. Anyone else experience this issue? Is there a known fix? I searched the forum but only see a problem related to I2C LCD screen. Mine is the regular 7 wire 16x2 display... any help would be greatly appreciated!

In the previous chapter, we have discussed how a character LCD is interfaced with a PIC microcontroller in 8-bit mode, where we used predefined characters stored in the LCD to display our data. In this article, we will learn more about the LCD and how we can create and use custom characters.

DDRAM or “Data Display Random Access Memory” is the working data buffer of the display. Each character on the display has a corresponding DDRAM location and the byte loaded in DDRAM controls which character is displayed.

CGROM or “Character Generation Read Only Memory” holds all the standard patterns for the 5 x 7 dot matrix characters. For instance, if you want to display character “A”, you would send ASCII code 65 (decimal) to the DDRAM. The display controller looks up the pattern of dots to display for this code in the CGROM and lights up the ones appropriate for “A”. The CGROM contents depend on the particular character set and model of display, US, Chinese etc. and cannot be changed.

CGRAM or “Character Generation Random Access Memory” allows the user to define special supplementary non-standard character types that are not in the CGROM. You can load your own dot pattern shapes and call these up for display.

For making custom patterns we need to write values to the CGRAM area defining which pixel to glow. These values are to be written in the CGRAM address starting from 0x40. CGRAM has a total of 64 Bytes. For LCD using 8×5 dots for each character, you can define a total of 8 user defined patterns (1 Byte for each row and 8 rows for each pattern).

To build a custom character we have to make a pixel-map of 8×5 and get the decimal value or hex value for each row. The bit value is 1 if the pixel is glowing and the bit value is 0 if the pixel is off. The final 8 values are loaded to the CGRAM one by one. The last row is usually left blank (0x00) for the cursor. If you are not using cursor then you can make use of that 8th row to get a bigger pattern.

We need to put these values in CGRAM. The CGRAM address starts from 0x40. We can store the data in any of the 8 available positions. To store this pattern in CGRAM we need to use a pointer containing the address of the pattern and the location at which we want to store the pattern.

Let’s say we want to write the Man pattern at second pattern location (At address location 0x48). We need to call the above function specifying the pattern to store and the decided position.

Custom characters are assigned fixed display codes from 0 to 7 for pattern stored in the location pointed by CGRAM address 0x40, 0x48, 0x56… and so on. So, if the user wants to display second pattern (pattern stored at CGRAM address 0x48), simply call the data function with value 1 as an argument at a desired location in the LCD.

To display the sequence in the LCD, we need to specify the position on LCD and which pattern to display at the position. Provide adequate delay in between frames to observe the sequence distinctly.