updated sample source

rewrote and simplified logic, added more interesting
text to be displayed which changes, added comments.

project10/i2c_1602lcd.c

@@ -10,7 +10,6 @@
 #include <wiringPiI2C.h>
 #include <string.h>
 
-int LCDAddr = 0x3f;//IIc LCD address
 int BLEN = 1;//1--open backlight.0--close backlight
 int fd;//linux file descriptor
 
@@ -24,48 +23,43 @@ void write_word(int data){
     wiringPiI2CWrite(fd, temp);
 }
 
-//send command to lcd
-void send_command(int comm){
-    int buf;
-    // Send bit7-4 firstly
-    buf = comm & 0xF0;
-    buf |= 0x04;            // RS = 0, RW = 0, EN = 1
+void sendNibble (int rs, int rw, int data)
+{
+    int buf = (data & 0x0F) << 4;  // data nibble in upper nibble of byte
+
+    // set the command pins data in the lower nibble of byte
+    buf |= 0x04;            // EN = 1, RW = 0, RS = 0
+    buf |= (rs) ? 0x01 : 0; // set RS value
+    buf |= (rw) ? 0x02 : 0; // set RW value
     write_word(buf);
+
     delay(2);
+
     buf &= 0xFB;            // Make EN = 0
     write_word(buf);
+}
+
+//send command to lcd
+void send_command(int comm){
+    // Send bit7-4 firstly
+    sendNibble (0, 0, comm >> 4);
 
     // Send bit3-0 secondly
-    buf = (comm & 0x0F) << 4;
-    buf |= 0x04;            // RS = 0, RW = 0, EN = 1
-    write_word(buf);
-    delay(2);
-    buf &= 0xFB;            // Make EN = 0
-    write_word(buf);
+    sendNibble (0, 0, comm);
 }
 
 //send data to lcd
 void send_data(int data){
-    int buf;
     // Send bit7-4 firstly
-    buf = data & 0xF0;
-    buf |= 0x05;            // RS = 1, RW = 0, EN = 1
-    write_word(buf);
-    delay(2);
-    buf &= 0xFB;            // Make EN = 0
-    write_word(buf);
+    sendNibble (1, 0, data >> 4);
 
     // Send bit3-0 secondly
-    buf = (data & 0x0F) << 4;
-    buf |= 0x05;            // RS = 1, RW = 0, EN = 1
-    write_word(buf);
-    delay(2);
-    buf &= 0xFB;            // Make EN = 0
-    write_word(buf);
+    sendNibble (1, 0, data);
 }
 
 //initialize the lcd
-void init(){
+void init1602 (void)
+{
     send_command(0x33); // Must initialize to 8-line mode at first
     delay(5);
     send_command(0x32); // Then initialize to 4-line mode
@@ -79,21 +73,24 @@ void init(){
 }
 
 //clear screen
-void clear(){
+void clear1602(void)
+{
     send_command(0x01); //clear Screen
 }
 
 //Print the message on the lcd
-void write(int x, int y, char data[]){
+void write(int xCol, int yRow, const char data[])
+{
     int addr, i;
     int tmp;
-    if (x < 0)  x = 0;
-    if (x > 15) x = 15;
-    if (y < 0)  y = 0;
-    if (y > 1)  y = 1;
+    if (xCol < 0)  xCol = 0;
+    if (xCol > 15) xCol = 15;
+    if (yRow < 0)  yRow = 0;
+    if (yRow > 1)  yRow = 1;
 
-    // Move cursor
-    addr = 0x80 + 0x40 * y + x;
+    // Move cursor to either line 1 or line 2
+    // line 1 -> 0x80 + xCol, line 2 -> 0xC0 + xCol
+    addr = 0x80 + 0x40 * yRow + xCol;
     send_command(addr);
 
     tmp = strlen(data);
@@ -120,19 +117,36 @@ void print_info()
     printf("Program is running...\n");
     printf("Press Ctrl+C to end the program\n");
 }
-int main(){
+
+int main(int argc, char *argv[])
+{
+    int LCDAddr = 0x27;//IIc LCD address
+
     //init I2C 
     fd = wiringPiI2CSetup(LCDAddr);
-    init();
+    if (fd < 0) {
+        printf ("Error: I2C setup for 1602 LCD failed.\n");
+        return 1;
+    }
+
+    init1602();
+
     print_info();
+
     write(0, 0, "Hi man.Welcome ");
     write(0, 1, "to osoyoo.com");
     delay(3000);
-    clear();
+    clear1602();
+
+    int iCount = 0;
     while(1){
-        write(0,0,"This is Lesson13");
-        write(0,1,"IIC LCD Test");
-        delay(1000);
+	char buf[24];
+
+        iCount++;
+	sprintf (buf, "Lesson13 cnt %d", iCount);
+        write(0, 0, buf);
+        write(0, 1, "IIC LCD Test");
+        delay(2000);
     }
     return 0;
 }