Using the Digital Discovery to Simulate an HD44780 Display

1. Make sure to download the Arduino sketch linked in the Inventory section of this guide.

2. Open the sketch and upload to the Arduino UNO. The sketch will display some short content received over the serial port on the LCD. Then the LCD should be connected to the Arduino module. All the connections are standard for 4-bit operation without reading the busy flag and are described in example Arduino sketch. The circuit is as follows:

LCD RS pin to digital pin 8
LCD Enable pin to digital pin 9
LCD D4 pin to digital pin 4
LCD D5 pin to digital pin 5
LCD D6 pin to digital pin 6
LCD D7 pin to digital pin 7
Backlight control to digital pin 10
LCD R/W pin to ground
10K resistor to +5V and ground
Wiper to LCD VO pin (LCD pin 3)

3. If using a different LCD module then the Arduino code should be adjusted as required before uploading and connecting. Initialize the library by associating any needed LCD interface pin with the Arduino pin number it is connected to.

const int rs = 8, en = 9, d4 = 4, d5 = 5, d6 = 6, d7 = 7, bl = 10;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

4. After resetting the device an “LCD TEST” message should appear on the display. If needed, a contrast should be adjusted. The following is how to connect the Digital Discovery to the HD44780 LCD:

Note: Ground should be connected before any other connections are made.

Digital Discovery GND to the LCD GND
Digital Discovery DIN0 to the LCD EN
Digital Discovery DIN1 to the LCD RS
Digital Discovery DIN2 to the LCD D4
Digital Discovery DIN3 to the LCD D5
Digital Discovery DIN4 to the LCD D6
Digital Discovery DIN5 to the LCD D7

Data sent to the HD44780-compatible display can be seen using WaveForms software and the Logic Analyzer instrument. In the Logic Analyzer, add a bus with clock on rising edge of the EN signal. Next, add the RS signal as a separate signal and set trigger mode to normal with triggering on a rising edge of the EN signal. After this is set up, run the Logic Analyzer and send one letter through the serial port. The letter will appear on the LCD and in the Logic Analyzer. At this point you will be able to see the four 4-bit nibbles that were transmitted, each on the rising edge of the EN line. Nibbles are “grouped” to form an 8-bit number. The state of the RS line determines whether this 8-bit number is command RS low or data RS high. The command 0x01 (“clear display”) is sent followed by data 0x50 which is the letter “P” encoded in ASCII.

To test the example, run the Python script. If the Raw buffer or Data buffer are filling very quickly, the sample rate should be reduced. Be aware that a too-low sample rate may not “catch” all EN pulses which can be as short as 450 ns according to specification.

# sample rate = system frequency / divider, 100 MHz / 400 = 0.25 MHz
dwf.FDwfDigitalInDividerSet(hdwf, c_int(400))

Establish a serial connection with the Arduino. You may need to reset the Arduino if the connection is already established.

The “Int” indicator shows if the initialization was detected by the script. A value of “2” means that initialization was completed successfully and values of “0” or “1” indicate an incomplete process. If the display is already initialized when starting-up, the script user can set the SI or reset the CI initialization flag. The “Nib” indicator represents if an even number of nibbles have been received. Even is indicated with a “0” and odd with a “1”. If errors are generated, the user can also use the CN and SN buttons to manually adjust that flag. After sending some data to the Arduino through the serial port, the data is displayed on the LCD and in the user interface created by the Python script.