String array display on LCD using PIC MCU

Question

I want to display certain messages on an LCD using a PIC MCU (16F887) and mikroC PRO for programming.

I have stored the words in a 2D string array like in the following program:

char text[21][11]={"GAS","DETECTED","MODE","SENSOR","TEST","SPRAY","GAS","ON",
                    "THE","PERFECT!!!","OVER","DOES","NOT","RESPONDE","PLEASE",
                    "REDO","FAILURE","SUSPECTED","CAUTION","NO"};

Now, for example, if I want to display "GAS DETECTED" I proceed as follows:

lcd_out(1,1,text[1][11]);
lcd_out(1,13,text[2][11]);

Here, I have noticed that:

1. When I simulate the program as above I get a message error that says "Not enough RAM 'text'", So I understood that RAM is saturated, and I have declared my array with the const modifier as follows:

const char text[21][11]={"GAS","DETECTED","MODE","SENSOR","TEST","SPRAY","GAS","ON",
                    "THE","PERFECT!!!","OVER","DOES","NOT","RESPONDE","PLEASE",
                    "REDO","FAILURE","SUSPECTED","CAUTION","NO"};

Here again, I did not get the message error, but when I load the program to the PIC, nothing is displayed on the LCD.

NB: The LCD connections are correct, and it works perfectly with simple programs like: Lcd_out(1,1,"Hello");

Could anyone explain to me where the problem is, and what the best solution is to display a sentence on a 2x16 LCD?

Answer 1

The correct usage is lcd_out(1, 1, text[0]) to display "GAS", lcd_out(1, 13, text[1]) to display "DETECTED".

Edit: I have never used either a PIC processor or MikroC before, so I had to do a little research. The Lcd_Out function prototype is:

void Lcd_Out(char row, char column, char *text)

It appears the PIC processor needs to know exactly where data resides (Flash, SRAM, EEPROM) in order to access it. The prototype for Lcd_Out function indicates it expects the data to be in volatile (SRAM) memory. The compiler rightfully gave an error to my solution because the strings are in flash memory. What you will need to do is use the other Lcd_ functions instead of Lcd_Out, for example:

int i;

Lcd_Cmd(_LCD_FIRST_ROW); /* Set cursor to first row */

for (i = 0; text[0][i] != 0; ++i) /* Loop until end of string */
    Lcd_Chr_Cp(text[0][i]); /* Write next character in string */

Lcd_Cmd(_LCD_SECOND_ROW); /* Same process for second string */

for (i = 0; text[1][i] != 0; ++i)
    Lcd_Chr_Cp(text[1][i]);

Answer 2

First, don't declare the size of the strings: you are wasting space, and you'll have issues when you change some text and it becomes longer. Use a char * rather than char[11] for each string.

You should probably not declare the size of the array either, the compiler will allocate an array of the size required for the number of strings.

Just write:

const char *text[] =
{
    "GAS",
    "DETECTED",
    "MODE",
    "SENSOR",
    "TEST",
    "SPRAY",
    "GAS",
    "ON",
    "THE",
    "PERFECT!!!",
    "OVER",
    "DOES",
    "NOT",
    "RESPONDE",
    "PLEASE",
    "REDO",
    "FAILURE",
    "SUSPECTED",
    "CAUTION",
    "NO",
};

This will give you an array of pointers.

Next, when you want to print the first string, use text[0]. Don't add another index (it would return the character at that position, not the string). And indexes in C are 0-based, so the first item in an array is index 0, the second is index 1, etc.