lcd displays that are compatible with the hitachi hd44780 driver manufacturer

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Modern Character LCD display modules have been possible since 1987 when Hitachi introduced the HD44780 LCD controller. Since then, Hitachi no longer manufactures this integrated circuit (IC), but modern LCD controller ICs make it a point to be HD44780-compatible.

The character LCD display modules offered by Crystalfontz America Inc. are no exception to this compatibility standard. This assures backwards compatibility with existing product infrastructure for our customers.

From time to time, we are asked to find a suitable replacement for an older LCD display. When our customer sent us the just-barely functional display in question to help verify we did have a compatible display we were delighted (in only the way Engineers can get delighted) that the old display had an old-school HD44780 controller.

Since the display was operational, we were able to find a suitable replacement for our customer. A few modifications were necessary to drive the backlight properly in the device the display is for, but otherwise, the display was functionally the same, thanks to the HD44780 compatible controller.

This gave us an opportunity to see the changes in how Character LCD displays are manufactured and assembled. The controller and drivers ICs are no longer discreet IC — they are bonded to the PCB and then covered with ‘blobs” to protect them. (Learn more about blobs on LCDs.) The improvements in PCB layout, design, and manufacturing are very apparent.

We invite you to contact our helpful customer support team via chat, phone, or email — to see what display will best suit your needs or answer any questions our LCD, TFT, and OLED modules.

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.

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.

As of August 2018 the State of California has changed the requirements of the �Prop 65� law. We now must list on our website any possible chemicals the can cause cancer, birth defects or reproductive problem.

To put it simply we are a small company and do not have the resources to test every single part, so we list every thing as hazardous. Please recycle all electronic parts responsibly and under no circumstance eat, drink or smoke these parts and wash your hands after touching!

As of August 2018 the State of California has changed the requirements of the �Prop 65� law. We now must list on our website any possible chemicals the can cause cancer, birth defects or reproductive problem.

To put it simply we are a small company and do not have the resources to test every single part, so we list every thing as hazardous. Please recycle all electronic parts responsibly and under no circumstance eat, drink or smoke these parts and wash your hands after touching!

HD44780 compatible LCDs come in many shapes and sizes and two very common ones are the 16×2 and 20×4 characters. Although most screens come with a back light some do not. And although the original interface is parallel some screens come with an I2C adapter/daughter board pre attached (you can buy the I2C adapters separately).

LCDs without the adaptor require 8 or 12 connections (see 4bit / 8bit below) and screens with the adaptor only need 4 connections. This makes the modules with the I2C adaptors far easier to wire up.

A key benefit of using a library is that we do not need to care that much about the technical details or timings when using the display. The library happily does all of this for us. On the downside, when different libraries try to use the same resources it can be very difficult to find the problem.

The Arduino IDE comes with a basic LiquidCrystal library pre installed. This works with parallel interfaces only. It works fine but has some limitations.

There are various other Character LCD libraries available. The two I use and recommend are NewLiquidCrystal by Francisco Malpartida and Bill Perry’s Extensible hd44780 LCD library.

NewLiquidCrystal is a collection of libraries that can handle almost all HD44780 compatible displays. It has a number of benefits over the default library, including the ability to handle screens with an I2C adapter. NewLiquidCrystal is a replacement for the default library so the default library has to be removed from the Arduino’s libraries folder.

Print characters or numbers to the screen. Starts printing at the current cursor position. When a character is printed, the cursor position is updated to the next position automatically (either left or right depending on the settings). For example. With the default setting of leftToRight, if the cursor is set to 0,0 and you print “HELLO”. The cursor will be set to position 5. If you then print “GOODBYE”, GOODBYE will automatically start at position 5 and you will see “HELLOGOODBYE” on the screen.

Something to note. When printing numbers the string “1000” prints exactly the same as the value 1000. This is due to the library converting the number 1000 to the string “1000” before displaying on the screen. If you want to use a numeric value to print an alphanumeric character (for example 65 for “A”) use lcd.write();

lcd.println() is part of the print class and inherited in the library by default. Although it works in that the characters are displayed, the command appends the nl and cr characters to the end of the string. The LCD will try to display these normally non-printable characters. Some screens may just show empty spaces, other may show characters from the extended character set. There is no reason to use this command with LCDs

Coordinates start at 0 so for a 16×2 screen X goes from 0 to 15 (16 places in total). Y goes from 0 to 1 (2 rows). The screens are top down, left to right. This means position 0,0 is at the top left and position 15,1 is bottom right.

Scrolls the text over as new characters are printed. Each new character is displayed at the same cursor position and existing text is moved across. The direction of scroll can be set using scrollDisplayLeft or scrollDisplayRight. While autoScroll is active the cursor position in not increased or decreased as new characters are printed.

Most HD44780 compatible LCDs have 8 memory locations that can store user defined characters. To create a character place the character definition data in a byte array and then pass the array to the library.

To get started we will use a 16×2 JHD162A display in 4bit mode with the HelloWorld example from the Arduino IDE. The JHD162A is a very popular, cheap and easy to source 16×2 display.

The RS pin is the Register Select pin. The HD44780 can accept 2 kinds of data; text and commands. The RS pin tells the HD44780 which type data the current value is. Set the pin LOW for command data and HIGH for ascii character data. The pin actually controls where in the LCDs memory data is written to. There are 2 options.

The R/W pin is a Read/Write pin. Apart from writing to the screen you can also read from it and the R/W pin controls which one you are doing. Set R/W LOW for write and HIGH for read. Note: the default Arduino LCD library only allows you to write and why most getting started circuits show this pin connected directly to GND (mine included).

VEE controls the screens contrast and is generally connected to a potentiometer allowing the contrast to be adjusted. In these examples I am using a fairly large 10K pot but small trimmers can also be used.

HD44780 compatible displays can use 4bit mode or 8bit mode. In 4bit mode 4 pins are used for the data and in 8bit mode 8 pins are used. In 4bit mode the 8bits are split in to 2 4bit values and sent to the lCD separately. This takes extra time. Of course, we are talking milliseconds so you are unlikely to notice any difference.

Update: There does not appear to be any speed difference between 4bit mode and 8bit mode when using the default LiquidDisplay library. This may be due to the library not using the R/W pin correctly or it may be due to how the Arduino maps pins. Have now found further reference over at PRJC. The page also lists the LiquidDisplayFast library. So if you really need the screen to update quickly the LiquidDisplayFast library or the NewLiquidCrystal library (5 times faster) may be the way to go. There is also a difference when using the NewLiquidCrystal library which appears to use the RW flag correctly and can be up to 5 times faster than the default library.

It all comes down to pins, if you want to have an LCD but need the pins for other things go 4bit. If speed is important and you don’t need the pins, go 8bit. If pins are really important and you can’t spare even the ones required for 4bit then you should consider using a I2C adapter. This is slower still but uses far fewer pins (just 2). See below for more.

Open the IDE, copy the below sketch and paste in to the IDE and upload. If everything is OK you should see the LCD come to life and display “hello, world!” on the top line. On the bottom line you should see a count slowly count up in seconds.

Display the number of seconds since the Arduino started or was reset (millis() divided by 1000 equals seconds). numeric values are automatically converted to ascii before displaying. This means the number 1 is played as “1”.

When using a LCD with a parallel interface you have full control over the back light. This not only includes turning it on and off but also dimming it. Turning on and off is simply a case of connecting to power or not. To make back light appear dimmer we can use another potentiometer or PWM.

The back light of the JHD162A is a LED matrix, this means we can make them dimmer by increasing the resistance, either by using different resistor values or by using a potentiometer.

To allow the Arduino to control the back light we use a PWM signal. The PWN signal turns the LED back light on and off very quickly which, to the human eye, makes it look dimmer.

It is tempting to connect the back light power connector directly to an Arduino pin and this may work. But we don’t know how much current the back light draws and the data sheet does not always say. So you shouldn’t do it. Although Arduino pins can supply a maximum of 40mA, 40mA is the maximum for very short periods of time. Arduino pins cannot provide the full 40mA for any length of time. A better way is to use a transistor as a switch. In this example I am using a 2N222 NPN transistor on the LOW side (GND side). You could also use a PNP transistor on the HIGH side (+5V side).

I modified the Hello World sketch to add PWM control. The following sketch increases the PWM value by 10 every loop. This increases the back light brightness (0 is off, 255 is full on). You may notice that the value of brightness never gets to 255!

Here we are using D6 to control the back light brightness and changing the value of brightness in analogWrite(backLightPWMpin, brightness) changes the back light intensity.

If you have read through the commands in the above table you may have noticed that the NewLiquidCrystal library has this function built in. The setBacklight() command does exactly the same thing in the same way.

First let the library know what pin you are using with setBacklightPin() then set the brightness using setBacklight(). As with analogeWrite 0=off and 255 = full on.

The I2C daughter board is a small add on that converts I2C communication to parallel communication. Among the various different I2C adapters there are two common ones. One with a fixed address and one with jumpers/solder pads that allow you to change the address.

Modules with fixed addresses usually have an address of HEX 27 (0x27) but can also have 0x20 or 0x3F (one of the first adapters I bought was set to 0x3F but I haven’t come across any since).

If you cannot get the screen to work and you think you have the wrong address use an I2C scanner to find the screen’s address or use the diagnostic tool within the Extensible hd44780 LCD library (see below).

On the I2C adaptor, the back light is controlled by two pins. Short the pins with a jumper to enable the back light. Remove the jumper to disable the back light. On some adapters the positive pin connects directly to the controller chip and on others it goes to a transistor.

On LCDs with the I2C adapter, the back light cannot be dimmed. It can be on or off only. To enable the Arduino to control the back light, connect the back pins on the I2C board to a transistor and then the transistors base pin to the Arduino (via a 1K ohm resistor).

All the I2C boards I have use the PCF8754 chip, either the Philips PCF8754T or the NXP PCF8574/PCF8574A. The devices without an ‘A’ in the suffix have a base address of 0x20 and a range from 0x20 to 0x27. The devices with an ‘A’ in the suffix have a base address of 0x38 and a range from 0x38 to 0x3F.

Once you have everything connected, LCDs with a I2C adaptor act pretty much like those without. Using the library is the same and the commands are the same.

When the pin data is not given, the library will add the default pin mapping for the LCDXIO LCD/expander backpack sold by Francisco Malpartida’s ElectroFun company and unfortunately this is not the same as other I2C adapters and so we need to specify the pins.

When using an I2C adaptor, we can turn the back light on and off with the lcd.backlight() and lcd.noBacklight() commands. No extra connections are required.

The following sketch displays Hello World on the LCD and then flashes the back light on and off every second. This uses the same circuit as above. Just SDA and SCL on pins A4 and A5.

Due to how the memory is allocated inside the LCD device, characters may not over flow as you expect. When characters over flow from line 1 they continue on line 3. When line 2 over flows the text continues on line 4.

Most HD44780 compatible LCDs have 8 memory locations that can be used for creating user defined characters. You create a custom character by putting the character data in to a byte array then passing the array to the library using createChar() command. Each character occupies a 5×8 grid

Although only 8 characters can be created at any one time, the characters can be redefined at anytime and creating new characters on the fly can give the appearance that more than 8 exist, although only 8 can be displayed at any one time.

Bill Perry’s Extensible hd44780 LCD library looks very promising. Extensible hd44780 LCD library can be downloaded from github. The library covers all the regular commands and includes a diagnostic sketch in the examples. Have an HD44780 LCD but can’t get it working or not sure how to initialise the library, run the diag sketch and it will tell you.

Using clear() is very slow. In many cases filling the screen with spaces is quicker. If speed is important, only update the parts of the screen that need updating and don’t write data if it has not changed.

There is an issue with the back light on some LCD shields. See this post in the Arduino forum. The Extensible hd44780 library works around the problem in software.

Good information about LCDs with I2C adapters at Arduino Info. The I2C LCD page also has information about other types of adapters. It is worth while checking out the whole site. Lots of good information about Arduino and Arduino compatible modules.

Reducing Arduino Pins: If you don’t have a I2C adaptor but have a 74HC595 and want to use less pins have a look at Juan Hernandez’s library that uses SPI and a 74HC595.

A new HD44780 LCD library by Bill Perry looks very promising. Extensible hd44780 LCD library can be downloaded from github. The library covers all the regular commands and includes a dianostic sketch in the examples. Have a HD44780 LCD but not sure how to initialise the library, run the diag sketch and it will tell you.

The following documentation describes a potential way to drive HD44780-style 16x2 character LCDs in graphics mode by using a synchronized updating scheme and complementary special characters.

Character LCDs used in industrial machinery, test equipment and hobby projects are popular, long-lived and mostly based on Hitachi HD44780-style controllers (+ drivers) from multiple manufacturers:

The driving scheme for passive matrix displays depends on the arrangement of character groups and format (e.g. 5x8, 5x10, 5x11), but is most often seen to be 1:16-multiplexed with 1/5 level bias.

The 1:2 multiplex scheme below (taken from the NXP PCF2119 datasheet) conveys the idea in a more accessible fashion. STN pixels at the junction of row and column conductor stripes see a differential AC waveform. Small amplitudes don"t cause a pixel to switch, and in this case, pairs of frames must be generated complementarily to create a zero time average (no DC component).

With this in mind, the timing for a display with 1:16 multiplexing and 1/5 bias can be understood as cycling through all 16 rows, where only the first time slot associated with COM1 has the high levels contributing to cell switching.

Although HD44780-like controllers have an 8 bit parallel interface, the instruction decoding and memory access logic appears to be such that one command takes at least 37 µs at 270 kHz nominal clock speed, or 10 clock cycles. The write cursor (pointer) is post-incremented when a write command is performed, so at least one address update needs to precede or follow a burst write operation. Writing 16 consecutive characters costs a minimum of 170 clocks. Filling an 8x2 character region costs at least 180 clocks, highlighting the limitations of what is possible within the time duration of a single-line drive phase of 200 clocks.

In terms of organization, 16x2, 20x2 and 20x4 LCDs use additional drivers to add more column lines, which follow a bias scheme like the one discussed above. The application circuit below shows the daisy-chained configuration for up to 20x4 characters:

Note that only a 8x2 character block is driven by the controller itself. Pixel data for all remaining characters is transferred to daisychained driver ICs via a 3-wire synchronous serial interface.

This will be used later by inserting a resistor into the data (D) line from the controller to the first driver. A GPIO pin connected after the resistor is used for bi-directional interaction. Display controllers use a resistor-programmed internal oscillator, and injected data is synchronized to CL1, CL2 or M.

Just by looking at videos people have taken from their displays, tearing as a pre-requisite can be observed. As the bar graph is updated, blocks indicate data was updated during a frame.

The appetite for graphic memory access is perhaps best visible through the widespread fascination hobbyists and demoscene people have with the measly 8 custom characters available in all controllers. This well-documented feature is used by writing character code 0x00 .. 0x07 into DDRAM. The controller then gets pixel data from CGRAM and uses it analogous to CGROM data.

Although many controller manufacturers offer multiple CGROM variants (font sets) with special characters, there aren"t 2^40 different unique ones (128 GB) to display arbitrary 5x8 pixel blocks - needless to say the 40 bit character code might as well represent the pixel information itself.

If one could swap out a character before each line were serialized and sent to the column drivers however, each of 8 horizontal lines making up a 5x8 pixel character could be loaded from one of 32 characters. This subdivides the representation of an 5x8 arbitrary pixel block into 8 consecutively selected LUT characters. The image below shows placeholders for all LUT characters. The dark gray regions are ignored, while the relevant lines are drawn in black/light gray, depicting the required bit patterns.

These are exact matches, but some pixel combinations are left out. Luckily, there are still 8 custom characters available to complement the CGROM set.

With the exception of the first LUT line, all LUT lines have <= 8 missing characters, so CGRAM codes can be inserted, and CGRAM pixels defined accordingly by copying the sought-after 5-pixel combinations to their corresponding y positions. These are the custom characters derived from the A02 font set (with some artistic license, as 5-pixel lines of the same y position are interchangeable):

The following LUT example depicts how 5x8 graphics content is mapped to 8 LUT characters displayed in sequence, and of which only one line is used to compose the ouput on the LCD panel.

To investigate whether there is a window of opportunity to write LUT codes into DDRAM and to reset the DDRAM cursor periodically and synchronized to the bit pattern generation, an reduced section of the functional block diagram from the HD44780 datasheet is presented below.

DDRAM addresses come from the instruction decoder, as well as from the timing generator (not necessarily indicated in all datasheets). The 8 bit data bus is necessarily controlled by the MPU (or instruction decoder). As the data bus is shared, access is likely to be interleaved.

4-bit line positions (0..7 for 5x8 characters, 0..10 for 5x11) need to come from the timing generator, as the memory outputs are only 5 bit wide towards the serializer.

The timing generator and MPU need to be synchronized to ensure appropriate phasing of data transfers into the serializer unit. Some arrows are rather hand-waivy. The more familiar "reset" signal doesn"t point to anything in particular, and it is implied that it connects to multiple blocks. Both "Instruction decoder" arrows have an unspecified bit width, but they"re not 1 bit wide (not plausible for address data to counter). So essentially there is a possibility that multiple lines are routed to the Timing Generator block, allowing an operation to reset the Timing Generator. Hopefully DISPLAY ON/OFF triggers such a reset.

Other datasheets are even less clear about the actual function or existence of Instruction Decoder outputs and interconnectedness. Maybe a die shot would help to clarify.

This leads to believe that the Parallel/Serial converter unit is also buffered and in part controlled by the MPU / instruction decoder. Depending on the address counter (< 16), CGRAM 5-bit data is used instead of CGROM 5-bit data. Additionally, the order of DDRAM readout is dependent on the display layout stored in the MPU, so the MPU is continuously involved in loading DDRAM data.

The serializer needs to be filled with fresh data for every line, as the line selection already happens during CGRAM / CGROM access and no full CGROM/CGRAM 2D image is copied. The functional block diagram shows a 40 bit shift register connected to the serializer. Strangely, the "parallel/serial converter" has a 40 bit wide output bus, so it essentially stores the eight 5-bit values loaded from CGRAM/CGROM.

The maximum size is 80 displayed characters, each measuring 5x8 pixels, for a total of 3200 pixels. Divide that by the maximum of 16 COM lines and each line has to have 200 pixels. This number shows up above as the "200 clocks" for which one COM line is driven in a 1:16 multiplexing scheme. So without measuring, one can derive that the serializer is clocked at the full oscillator frequency. It seems plausible that the serializer would then run continuously but only fed a part of the time when displays are smaller.

We now also know that the MPU has 5 clock cycles to get the CGROM/CGRAM data into the parallel buffer of the parallel/serial converter, and for a 20x4 display, serializer data loading has to run continuously.

The MPU is thus twice as fast when transferring the data as one could write it into DDRAM. Timing-wise, one needs to start writing right at or behind the internal reading address. Assuming an instruction or data write operation takes 11 clocks, 16 LUT characters + 1 instruction byte can be written and processed, unlocking 16x2 * 5*8 graphics mode. That"s 80x16 (1280) pixels, give or take.

It should also be noted that when limiting oneself to an 8x2 character block and 1/16 multiplexing, DDRAM 0x00 .. 0x07 and 0x40 .. x047 can also be directly filled with custom chracters 0 .. 7. Instead of changing character codes in DDRAM, write operations can update CGRAM patterns in the corresponding custom character lines, creating full pixel access. The second set of rows (COM8..15) start at CGRAM line 0, 1, ... again, making custom characters a just-in-time video buffer.

Furthermore, when injecting data into the serial interface to the daisy-chained extension drivers, only 8 characters + 1 command byte need to be written, further relaxing the timing and creating leeway for "software" synchronization. The latter relies on the assumption that a DISPLAY ON/OFF command resets the row counter in the timing generator. HD44780-like controllers offer an external clock option for jitter- and drift-free operation, but adding wires for extension driver CL1, CL2, M and D lines seems a lot more useful. The timing seems to be too critical to rely on RC oscillator accuracy anyway, and even though that makes it an invasive modification, it is being rewarded with a pathway to 20x4 character graphic mode.

With a 4k7 resistor placed over a cut through the D line between main controller and the first auxiliary driver, a GPIO can be connected on the driver side for bidirectional I/O. CGROM or custom characters can then be read as they are being sent out to column drivers and synchronized to, before the GPIO is switched to push-pull mode, taking over the role as pixel data source.

Presenting pixel data to extension drivers only, and also using them for row driving, seems to have been a product reality around 1985, as the picture below shared by AVRFreaks user ossi evidences:

so there really should be nothing holding us back morally from modifying modern displays for pixel data injection synchronous to a clock provided by a controller.

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AMIS-30421 : Stepper Motor Controller The AMIS30421 is a micro stepping stepper motor bridge controller for large current range bipolar applications. The chip interfaces via a SPI interface with an external controller in order to control two external power NMOS H bridges. It has an on chip voltage regulator, current sensing, self adapting PWM controller and pre driver.

RH-053.3D/H6 : Isolated DC/DC Converters 1W 5Vin +/-3.3Vout +/-152mA SIP7. RECOM Power Econoline RK/H6 & RH/H6 DC/DC Converters RK/H6 & RH/H6: 1Watt SIP7 Single and Dual Output DC/DC Converters feature high 6.4kVDC isolation and an extended operating temperature range up to +90�C without derating, yet are lower cost than standard high isolation converters.

Blue 16x2 LCD module featuring 2 rows consisting each of 16 characters. The module is compatible with the Hitachi HD44780 controller, and is commonly used in Arduino and other microcontroller projects.

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