AVR-GCC LCD library – mixed pin support

Some time ago we have posted alphanumeric AVR-GCC LCD library. It works fine in 8-bit and 4-bit modes. But it has some limitations that some people may find annoying. One of them is requirement that LCD pins has to be byte aligned for instance in 8 bit mode LCD_D0 … LCD_D7 pins has to be connected to AVR single AVR port. Similar situation is with 4-bit mode where LCD data pins has to be connected to single port 4, 5, 6 and 7 pins. For both modes control pins RS, RW and E has to be connected to single port.

And this is how most LCD libraries work when you try to look for one in the internet. In reality things may be a bit different each microcontroller pin has at least several alternative functions available like ADC, INT, I2C, USART and if project requires using one or another and you still need LCD standard libraries won't work as most likely you wont be able to get all particular port pins connected to LCD. You gotta use whats left. This is why I decided to find a little time and modify LCD library to support these cases. Didn't want to write everything from scratch or change its functionality – just wanted it work with existing projects but have more freedom with new ones. So basically I left standard 8-bit and 4-bit same. The main change is adding two more modes: 8-bit mix and 4-bit mix. These modes allow connected LCD to any free pins of microcontroller.

Configuring LCD for 4-bit mixed pin mode

Lets look what you need to start using these features. We can do this by selecting a simple example. This time 4-bit mixed mode:

As you can see LCD pins are connected to Atmega328P in following way:

RS - > PB5

RW - > PD1

E - > PD2

D4 - > PD4

D5 - > PC2

D6 - > PD6

D7 - > PB0

So we get unaligned situation. Firs of all we need to edit pin assignments in lcd_lib.h. First of all uncomment one of following defines that indicate the mode chosen

//LCD 4 bit interface is used (single port pins)

//#define LCD_4BIT

//LCD 8 bit interface is used (single port pins)

//#define LCD_8BIT

//LCD 4 bit interface is used (mixed port pins)

#define LCD_4BIT_M

//LCD 8 bit interface is used (mixed port pins)

//#define LCD_8BIT_M

This time we use LCD_4BIT_M

Then we need to associate LCD pins with port pin numbers. If LCD_RS is connected to PB5 pin then we write 5:

#define LCD_RS 5 //define MCU pin connected to LCD RS

#define LCD_RW 1 //define MCU pin connected to LCD R/W

#define LCD_E 2 //define MCU pin connected to LCD E

#define LCD_D0 0 //define MCU pin connected to LCD D0

#define LCD_D1 1 //define MCU pin connected to LCD D1

#define LCD_D2 2 //define MCU pin connected to LCD D2

#define LCD_D3 3 //define MCU pin connected to LCD D3

#define LCD_D4 4 //define MCU pin connected to LCD D4

#define LCD_D5 2 //define MCU pin connected to LCD D5

#define LCD_D6 6 //define MCU pin connected to LCD D6

#define LCD_D7 0 //define MCU pin connected to LCD D7

And now we have to define port and data direction register for each pin. As pins may be connected to different ports – we need to work with individual pins. We edit this part:

#ifdef LCD_4BIT_M || LCD_8BIT_M //8- bit or 4 - bit mode

#define LDPRS PORTB //RS pin assignment

#define LDDRS DDRB

#define LDPRW PORTD //RW pin assignment

#define LDDRW DDRD

#define LDPE PORTD //E pin assignment

#define LDDE DDRD

#define LDPD0 PORTD //D0 pin assignment

#define LDDD0 DDRD

#define LDPD1 PORTD //D1 pin assignment

#define LDDD1 DDRD

#define LDPD2 PORTD //D2 pin assignment

#define LDDD2 DDRD

#define LDPD3 PORTD //D3 pin assignment

#define LDDD3 DDRD

#define LDPD4 PORTD //D4 pin assignment

#define LDDD4 DDRD

#define LDPD5 PORTC //D5 pin assignment

#define LDDD5 DDRC

#define LDPD6 PORTD //D6 pin assignment

#define LDDD6 DDRD

#define LDPD7 PORTB //D7 pin assignment

#define LDDD7 DDRB

#endif

This is practically it. We can start using LCD as we did in old library version.

Configuring LCD for 8-bit mixed pin mode

To make sure things are working correctly lets set up project for 8-bit mixed mode. To do so we connect LCD as follows:

Again we uncomment following mode:

#define LCD_8BIT_M

Then assign pin numbers:

#define LCD_RS 5 //define MCU pin connected to LCD RS

#define LCD_RW 1 //define MCU pin connected to LCD R/W

#define LCD_E 2 //define MCU pin connected to LCD E

#define LCD_D0 0 //define MCU pin connected to LCD D0

#define LCD_D1 7 //define MCU pin connected to LCD D1

#define LCD_D2 1 //define MCU pin connected to LCD D2

#define LCD_D3 2 //define MCU pin connected to LCD D3

#define LCD_D4 4 //define MCU pin connected to LCD D4

#define LCD_D5 2 //define MCU pin connected to LCD D5

#define LCD_D6 6 //define MCU pin connected to LCD D6

#define LCD_D7 0 //define MCU pin connected to LCD D7

and finally we chose ports for each pin assigned pin:

#if defined (LCD_4BIT_M) || defined (LCD_8BIT_M)

#define LDPRS PORTB //RS pin assignment

#define LDDRS DDRB

#define LDPRW PORTD //RW pin assignment

#define LDDRW DDRD

#define LDPE PORTD //E pin assignment

#define LDDE DDRD

#define LDPD0 PORTC //D0 pin assignment

#define LDDD0 DDRC

#define LDPD1 PORTD //D1 pin assignment

#define LDDD1 DDRD

#define LDPD2 PORTC //D2 pin assignment

#define LDDD2 DDRC

#define LDPD3 PORTB //D3 pin assignment

#define LDDD3 DDRB

#define LDPD4 PORTD //D4 pin assignment

#define LDDD4 DDRD

#define LDPD5 PORTC //D5 pin assignment

#define LDDD5 DDRC

#define LDPD6 PORTD //D6 pin assignment

#define LDDD6 DDRD

#define LDPD7 PORTB //D7 pin assignment

#define LDDD7 DDRB

#endif

Configuring LCD for normal 4-bit

In case you need to use LCD in byte aligned way like we used to do in old version of LCD library. To do so we need to uncomment mode:

#define LCD_4BIT

We still need to define pin numbers for for control and data pins.

#define LCD_RS 0 //define MCU pin connected to LCD RS

#define LCD_RW 1 //define MCU pin connected to LCD R/W

#define LCD_E 2 //define MCU pin connected to LCD E

#define LCD_D0 0 //define MCU pin connected to LCD D0

#define LCD_D1 1 //define MCU pin connected to LCD D1

#define LCD_D2 2 //define MCU pin connected to LCD D2

#define LCD_D3 3 //define MCU pin connected to LCD D3

#define LCD_D4 4 //define MCU pin connected to LCD D4

#define LCD_D5 5 //define MCU pin connected to LCD D5

#define LCD_D6 6 //define MCU pin connected to LCD D6

#define LCD_D7 7 //define MCU pin connected to LCD D7

Then we only need to define data and control ports as follows:

#if defined (LCD_4BIT) || defined (LCD_8BIT) //if aligned mode

#define LDP PORTD //define MCU port connected to LCD data pins

#define LCP PORTD //define MCU port connected to LCD control pins

#define LDDR DDRD //define MCU direction register for port connected to LCD data pins

#define LCDR DDRD //define MCU direction register for port connected to LCD control pins

#endif

same situation with normal 8 bit mode.

It is obviously that in pin aligned mode LCD update is faster as either 4-bit or 8-bit mode accepts data faster – byte or nibble operation. In mixed mode each individual pin needs to be set separately. This increases number of instructions used to transfer byte. For instance in order to send a byte in LCD_8BIT_M mode I used a helper function:

static void LCDMix_8Bit(uint8_t data)

{

if((data)&(0b10000000)) LDPD7 |=1<<LCD_D7;

else LDPD7 &=~(1<<LCD_D7);

if((data)&(0b01000000)) LDPD6 |=1<<LCD_D6;

else LDPD6 &=~(1<<LCD_D6);

if((data)&(0b00100000)) LDPD5 |=1<<LCD_D5;

else LDPD5&=~(1<<LCD_D5);

if((data)&(0b00010000)) LDPD4 |=1<<LCD_D4;

else LDPD4 &=~(1<<LCD_D4);

if((data)&(0b00001000)) LDPD3 |=1<<LCD_D3;

else LDPD3 &=~(1<<LCD_D3);

if((data)&(0b00000100)) LDPD2 |=1<<LCD_D2;

else LDPD2 &=~(1<<LCD_D2);

if((data)&(0b00000010)) LDPD1 |=1<<LCD_D1;

else LDPD1&=~(1<<LCD_D1);

if((data)&(0b00000001)) LDPD0 |=1<<LCD_D0;

else LDPD0 &=~(1<<LCD_D0);

}

Where every bit in data byte is tested and then corresponding port pin is set or reset. Generally speaking if your application simply indicates information that doesn't have to be updated frequently any mode is fine. But if you use LCD for dynamic indication like animations or other fancy way that needs fast LCD update then probably chose normal 8-bit mode or at least 4-bit. If you find errors or difficulties to use this lib, fell free to post a comment.