Problem with character LCD on Cyclone III FPGA Development Kit

[Altera_Forum]

Hello, 

 I am writing because I have a problem with the character LCD on Cyclone III FPGA Development Kit. I cannot write anything on it, I always have the first line completely black, and the second line completely empty.  I read carefully the documentation and previous posts on the forum about similar problem, and I know that there is an error on the Altera documentation about the enable pin (AC24 instead of AB24). So, I do not understand why that does not work.  Attaching, I put the schematic file of quartus, the system build with sopc builder, and the properties of the nios project.  I first try with the following simple program :  # include <stdio.h> // Needed for printf# include "system.h"# include "altera_avalon_pio_regs.h" int main (void) { IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0x35); // Display a known value on leds printf("Hello\n"); IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0xA2); // Display a known value on leds while(1); } My leds display well 0xA2 at the end, but nothing on LCD.  After I try using fprintf, with the following program : # include <stdio.h> // Needed for printf# include <unistd.h> // Needed for usleep# include "system.h"# include "altera_avalon_pio_regs.h" int main (void) { int nbChar; FILE * lcd; lcd = fopen(LCD_NAME, "w"); // Open the LCD device if (lcd == NULL) // Test the success of the file opening by displaying value on leds IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0x86); else IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0x3C); usleep(5000000); // Pause 5s to read the value on leds nbChar = fprintf(lcd, "Hello\n"); // Printf something on LCD and get the number of characters written IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0xFF & (nbChar >> 24)); // Display on leds the value returned by fprintf (1st 8 bits) usleep(5000000); // Pause 5s to read the value on leds IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0xFF & (nbChar >> 16)); // Display on leds the value returned by fprintf (2nd 8 bits) usleep(5000000); // Pause 5s to read the value on leds IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0xFF & (nbChar >> 8)); // Display on leds the value returned by fprintf (3rd 8 bits) usleep(5000000); // Pause 5s to read the value on leds IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, 0xFF & (nbChar >> 0)); // Display on leds the value returned by fprintf (4th 8 bits) usleep(5000000); // Pause 5s to read the value on leds while(1); } The opening of the file succeed since I see 0x3C on the leds, and the value returned by the fprintf function is well 6. But I still have nothing on LCD.  If someone have an idea of the cause of this problem, because I really don't see what it can be.  Thanks in advance  Jérôme

[Altera_Forum]

Your code should work. If not, I will check two things: 

 1. Did you connect the LCD external pins (not in SOPC, but in top VHDL file)?  LCD_ON, -- Power ON/OFF   LCD_BLON, -- Back Light ON/OFF   if not, your LCD software may be working, but you will not see anything in the real LCD.   2. Maybe you need a initialization sequence for the LCD.    ///// LCD control: //////////////////////////////////////////////////////  // From: http://www.altera.com/support/examples/nios2/exm-micro_mutex.html  // ESC sequences:  // From: http://www.isthe.com/chongo/tech/comp/ansi_escapes.html  // ESC[#;#H Moves the cursor to line# , column#  // ESC[2J Clear screen and home cursor  // ESC[K Clear to end of line # define ESC_TOP_LEFT "[1;0H" # define ESC_BOTTOM_LEFT "[2;0H" # define LCD_CLR "[2J" # define LCD_CLR_LINE "[K"  static unsigned char ESC = 0x1b; // Integer ASCII value of the ESC character     void LCD_hello(void)  {   FILE* LCD;     LCD = fopen ("/dev/lcd", "w");     if (LCD == NULL) {   printf("LCD open failed\n");   } else {   printf("LCD open succeeded\n");     fprintf(LCD, "%c%s", ESC, LCD_CLR); // Clears LCD   fprintf(LCD, "LCD demo using\n");   fprintf(LCD, "Altera HAL in C");   }     fclose (LCD);  }

[Altera_Forum]

Hello, 

 There are no other external pins to connect to the LCD. The power is always given because it is directly connected to vcc (cf picture taken from board schematic).  I try with the initialization sequence but it doesn't change anything.

[Altera_Forum]

Sorry, I was thinking on DE2 boards, where enable signals should be connected outside SOPC to allow LCD operation. I don't know if it the same for Cyclone III kits.

[Altera_Forum]

Hello, 

 The problem is resolved. It was due to the hardware, because I put the data pins in output, whereas they have to be bidirectionnal.

[Altera_Forum]

This thread was a good find for me. I have been trying to get the character LCD panel working on a Cyclone III dev. kit and it would show no response. I knew about the enable pin documentation problem and was sure I had it wired properly. I came across this thread and then changed the data lines to bi-directional and now the character LCD works! Thanks for posting your find.

[Altera_Forum]

Hi, 

please can you tell me where to change the data lines to bidirectional. Please help, i need this to work.

[Altera_Forum]

Hi, 

It's the data pins that you connect to the LCD that have to be bidirectionnal, you do this in Quartus II. In the first picture attached, its LCD_DATA[7_0] (FPGA pins AB3, V6, V5, ..., AA4).

[Altera_Forum]

thank you for your reply. Im new in NIOS II. The LCD is now working. Now i need to write some charater on the LCD if i press a button and a different one when a relaese the button. FOr example: 

if button = 1 "HELLO" else "HI". i've write the follwing xode but is doesn't work. Can you hel me o n this. thank you.   int main (void) { // int nbChar; int botao; FILE * lcd; lcd = fopen(LCD_DISPLAY_NAME, "w"); // Open the LCD device     botao = IORD_ALTERA_AVALON_PIO_EDGE_CAP(USER_PB_BASE); if (botao == 1)  fprintf(lcd, "LASSE 2011\n"); else fprintf(lcd, "Second line 2011\n");  return(0); } 

[Altera_Forum]

Few ideas : 

1. Your program executes once and then exits. You have to put your test in a loop such as while(1). 2. When configuring the PIO Core, have you well enabled the edge capture ? On both edges ? 3. To detect both edges (button pushed and button released) you must change the if else operation you did, because the if tells you if you have a transition (it can be a rising or a falling edge), the else will thus be executed always if you don't touch the button. So inside, the if, you should have a second test to check the current value on the port to determine if it is was rising (1) or falling (0) transition.