I am struggling to understand this code [closed] - c

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I spent more time and struggling to understand this code.
I edited and manage to display the data on LCD but
I would like to understand it.
I have added some comment to the code to show my bit understanding.
// Control 16 character LCD (2x8 chars) with 4 bit interface
// Copyright (C) 2012 Joonas Pihlajamaa. Released to public domain.
// No warranties, use at your own responsibility.
#include <avr/io.h>
#define F_CPU 12000000UL // 12 MHz
#include <util/delay.h>
#define DATA_PORT_DIR DDRB // macro for data port direction
#define DATA_PORT PORTB //macro for data port
#define DATA_PORT_IN PINB //macro for data port pin
#define RW_PIN (1<<PD4) // PORTD Pin4 is defined as for RW
#define RS_PIN (1<<PD5) // PORTD Pin5 is defined as for RS
#define EN_PIN (1<<PD6) // PORTD Pin6 is defined as for EN
// macro or something else? confused?
#define SET_CTRL_BIT(pin) (PORTD |= pin)
#define CLEAR_CTRL_BIT(pin) (PORTD &= ~pin)
// assumes EN_PIN is LOW in the beginning
void lcd_write(char rs, unsigned char data)
{
if(DATA_PORT_DIR != 0xFF) // condition to test if DATA_PORT_DIR is true
//make DATA_PORT_DIR as output to write data to ldc
DATA_PORT_DIR = 0xFF;
CLEAR_CTRL_BIT(RW_PIN);
if(rs)
SET_CTRL_BIT(RS_PIN);
else
CLEAR_CTRL_BIT(RS_PIN);
DATA_PORT = data;
_delay_us(2);
SET_CTRL_BIT(EN_PIN);
_delay_us(2);
CLEAR_CTRL_BIT(EN_PIN);
}
unsigned char lcd_read(char rs)
{
unsigned char data;
if(DATA_PORT_DIR != 0)
DATA_PORT_DIR = 0;
SET_CTRL_BIT(RW_PIN);
if(rs)
SET_CTRL_BIT(RS_PIN);
else
CLEAR_CTRL_BIT(RS_PIN);
_delay_us(2);
SET_CTRL_BIT(EN_PIN);
_delay_us(2);
data = DATA_PORT_IN;
CLEAR_CTRL_BIT(EN_PIN);
return data;
}
void lcd_wait()
{
while(lcd_read(0) & 0x80); // wait until display is ready
}
void lcd_init()
{
_delay_ms(50); // wait for VDD to rise
lcd_write(0, 0x30);
_delay_ms(5);
lcd_write(0, 0x30);
_delay_ms(1); // _delay_us(120);
lcd_write(0, 0x30);
_delay_ms(1); // _delay_us(120);
lcd_write(0, 0x38); // 2 lines, normal font
_delay_ms(1);
lcd_write(0, 0xC); // display on
_delay_ms(1);
lcd_write(0, 1); // display clear
_delay_ms(1);
lcd_write(0, 0x6); // increment, don't shift
_delay_ms(1);
}
void lcd_puts(char * string)
{
char i;
lcd_write(0, 0x80); // move to 1st line
lcd_wait();
for(i=0; i<8; i++)
{
if(string[i] == '\0')
return;
lcd_write(1, string[i]);
lcd_wait();
}
lcd_write(0, 0x80+0x40); // move to 2nd line
lcd_wait();
for(i=8; i<16; i++)
{
if(string[i] == '\0')
return;
lcd_write(1, string[i]);
lcd_wait();
}
}
int main(void)
{
unsigned char i = 0;
char message[] = "nn Mississippi..";
DDRD = RS_PIN + EN_PIN + RW_PIN + LED_PIN; // Control outputs
DDRB = 0xFF; // Port B as DB0..DB7
lcd_init();
lcd_puts("Hello, World!!!");
_delay_ms(2000);
while(1)
{
if(++i >= 100)
i = 1;
if(i >= 10)
message[0] = i/10+'0';
else
message[0] = ' ';
message[1] = i%10+'0';
lcd_puts(message);
_delay_ms(1000);
}
return 1;
}

Answer 1

These define constants that have only the bit specified on
#define RW_PIN (1<<PD4) // PORTD Pin4 is defined as for RW
#define RS_PIN (1<<PD5) // PORTD Pin5 is defined as for RS
#define EN_PIN (1<<PD6) // PORTD Pin6 is defined as for EN
These Macros can then use the above can be used to set the bit (by OR'ing it on) or clearing the bit by using AND with the 1's complement of the constant (all bits on but one).
// macro or something else? confused?
#define SET_CTRL_BIT(pin) (PORTD |= pin)
#define CLEAR_CTRL_BIT(pin) (PORTD &= ~pin)
Here is what it looks that the write is doing: If first puts all the port bits in output mode (so it can write the data). It then sets RW pin low (I assume to put it in write mode) and resets the display (if rs is set) by toggling the RS bit. It then loads the data into the DATA_PORT and toggles the EN pin (I assume to load it).
// assumes EN_PIN is LOW in the beginning
void lcd_write(char rs, unsigned char data)
{
if(DATA_PORT_DIR != 0xFF) // condition to test if DATA_PORT_DIR is true
//make DATA_PORT_DIR as output to write data to ldc
DATA_PORT_DIR = 0xFF;
CLEAR_CTRL_BIT(RW_PIN);
if(rs)
SET_CTRL_BIT(RS_PIN);
else
CLEAR_CTRL_BIT(RS_PIN);
DATA_PORT = data;
_delay_us(2);
SET_CTRL_BIT(EN_PIN);
_delay_us(2);
CLEAR_CTRL_BIT(EN_PIN);
}
Here is what it looks that the read is doing: If first puts all the port bits in input mode (so it can read the data). It then sets RW pin high (I assume to put it in read mode) and resets the display (if rs is set) by toggling the RS bit. It then sets the EN bit and fetches the data from the DATA_PORT and turns the EN pin off again.
unsigned char lcd_read(char rs)
{
unsigned char data;
if(DATA_PORT_DIR != 0)
DATA_PORT_DIR = 0;
SET_CTRL_BIT(RW_PIN);
if(rs)
SET_CTRL_BIT(RS_PIN);
else
CLEAR_CTRL_BIT(RS_PIN);
_delay_us(2);
SET_CTRL_BIT(EN_PIN);
_delay_us(2);
data = DATA_PORT_IN;
CLEAR_CTRL_BIT(EN_PIN);
return data;
}
Is that enough for you to figure out what the rest is doing?