Using LCD module in Multisim 10

Question

Guys, I'm having trouble using the 20x2 LCD module. I interfaced it with an 8051 MCU module. And, I use the standard busy flag check(RS = 0, R/W = 1, d7 -> busy flag), but there are two problems:
1)  If the LCD is set to trigger on falling edge, the busy check routine goes on an infinite loop,I placed an oscilloscope at d7 and En. Each time there is a falling edge at En, the busy flag (d7) goes to zero(not busy) and immediately comes back to one (busy). This is the case always.
     Is this because there is some other setting to be changed or is the busy fuction not implemented?
2)  If the LCD is set to trigger on high state, when one character is sent the entire display gets filled by it and besides, the busy check doesn't iterate even once(Is the simulated LCD so fast that it can process faster than the CPU? wierd)
     I tried the same program in UMPS and it works fine. What can I do to make the LCD module work properly?

Answer 1

Hello PCA,
I've been strugling with LCD for some times now. I will be very glad if you could show me what you did with the code, and connectiion.
I'm going to paste the code in C, and the schematic of the circuit. Please tell me what is wrong with what im doind.
The LCD is always blank!
Here is my code:
#include <htc.h>
#include <stdio.h>
#define LCD_data P2
#define LCD_D7   P27
#define LCD_rs   P10
#define LCD_rw   P11
#define LCD_en   P12
/*static volatile unsigned char LCD_data @ 0xA0;
static volatile bit LCD_D7   @ 0xA7;
static volatile bit LCD_rs   @ 0x90;
static volatile bit LCD_rw   @ 0x91;
static volatile bit LCD_en   @ 0x92;*/
void LCD_init();
void LCD_busy();
void LCD_command(unsigned char );
void LCD_senddata(unsigned char );
void LCD_sendstring(unsigned char *);
void main()
    unsigned char msg[] = "HELLO WORLD";
     LCD_init();
     LCD_command(0x80);
     LCD_sendstring(msg);
    while(1); 
void LCD_init()
     LCD_data = 0x38;     //Function set: 2 Line, 8-bit, 5x7 dots
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
     LCD_data = 0x0D;     //Display on, Curson blinking command
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
     LCD_data = 0x01;     //Clear LCD
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
     LCD_data = 0x06;     //Entry mode, auto increment with no shift
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->L
     LCD_busy();
void LCD_busy()
     LCD_D7   = 1;           //Make D7th bit of LCD as i/p
     LCD_en   = 1;           //Make port pin as o/p
     LCD_rs   = 0;           //Selected command register
     LCD_rw   = 1;           //We are reading
     while(LCD_D7)
    {          //read busy flag again and again till it becomes 0
           LCD_en   = 0;     //Enable H->L
           LCD_en   = 1;
/*unsigned char i,j;
3+69
         for(i=0;i<50;i++)        //A simple for loop for delay
            for(j=0;j<255;j++);*/
void LCD_command(unsigned char var)
     LCD_data = var;      //Function set: 2 Line, 8-bit, 5x7 dots
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in instruction register
     LCD_en   = 1;        //Enable H->L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
/* Using the above function is really simple
 var will carry the command for LCD
 e.g.
 LCD_command(0x01);*/
void LCD_senddata(unsigned char var)
     LCD_data = var;      //Function set: 2 Line, 8-bit, 5x7 dots
     LCD_rs   = 1;        //Selected data register
     LCD_rw   = 0;        //We are writing
     LCD_en   = 1;        //Enable H->L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
/* Using the above function is really simple
 we will pass the character to display as argument to function
 e.g.
 LCD_senddata('A');*/
void LCD_sendstring(unsigned char *var)
     while(*var)              //till string ends
       LCD_senddata(*var++);  //send characters one by one
/* Using the above function is really simple
// we will pass the string directly to the function
// e.g.
// LCD_sendstring("LCD Tutorial");*/
Attachments:
schem.JPG ‏37 KB