Servo - June 2010

numbers, hex numbers and binary numbers can also be printed on the LCD display, but floating point numbers are currently not supported. The reason you can’t print floats using this technique is because the printf routine included with the free PIC18 C Student Compiler does not support floating point format.

The LCD driver code was developed using Microchip MPLAB and the PIC18 C compiler, and also uses IFI libraries. The code configures the VEX controller’s digital ports to outputs and initializes the Hitachi LCD controller. Once compiled, the lcd.hex file is generated that is used to program the VEX controller. (I have provided the lcd.hex file so that it can be used without having to compile it.) You’ll need the orange programming cable to download the firmware to the controller just like last time.

To include LCD support for your own applications, just add “#include lcd.h” to your C programs and lcd.c to your MPLAB project files.

Once you have downloaded the lcd.hex application using the IFI bootloader, the message “Hello World!!!” should appear. If it doesn’t work the first time, check the wiring and the power supply using a digital voltmeter; check for short circuits. Also make sure that the contrast is set correctly using the 10K trim pot.

This version of the LCD firmware includes a special LCD version of printf that can be used to display integer and hex values using the example shown in Listing 2. It uses the printf function to convert the integer value from binary to a formatted character string and then sends it directly to the LCD. The pause(n) function is used to delay in milliseconds between each printf call to give the user a chance to read the LCD display before it is overwritten by the next printf.

Displaying Floating Point Values

As previously mentioned, displaying 32-bit IEEE567 floating point values on the LCD is currently not supported in the C firmware that I provided, but is a feature that I would like to add in the future for my own VEX applications. It would require software to reformat the floating point numbers to ASCII text strings so that they can be printed on the LCD. In fact, I provided a routine in my previous article to display “fixed point” numbers on the numeric LED display that could easily be modified to display fixed point numbers and to also handle IEEE567 floating point numbers with exponents on higher resolution LCD displays.

Programming the VEX Controller

The next step is to download the lcd.hex application that is provided with this article into the controller and run it. Start by copying the led.hex file to your computer’s hard disk and place it in a folder. This is done by running the IFI bootloader and browsing to the directory that you created

FIGURE 5. This accelerometer display was generated using a Microchip dsPIC30F6014 development board graphics LCD display which uses the SPI interface. Notice that it does not have any problems with floating point when displaying the xyz tilt angles since the Microchip C30 compiler provides the necessary floating point libraries.

for the lcd.hex file. Turn the power switch on and download the led.hex file.

Once the lcd.hex file has been downloaded, the LCD should show “Hello World!!!” on the first line of the 2 x 16 character display.

Using Other LCD Displays Work with VEX?

Another character display that I connected to the VEX controller is shown in Figure 4. It is a surplus two line by 24 character display that I purchased online for around $10. The two lines and 24 character line length allow you to display even more information, including floating point values and extended text messages.

Graphics LCD Display Applications

Applications for new graphics displays are limitless and can be integrated into appliances, medical devices, automotive devices, and other embedded devices. The new QVGA interface provides access to high resolution graphics OLED displays and color LCD displays. Except for the serial RS-232 interface, these interfaces are more involved requiring more capable microcontrollers with built-in I2C and SPI peripherals.

The accelerometer display shown in Figure 5 was generated using a dsPIC30F6014 development board LCD display which uses the SPI interface. Notice that it does not have any problems with floating point when displaying the xyz tilt angles since the Microchip C30 compiler provides the necessary floating point libraries.