Embedded Systems Design with the Atmel AVR Microcontroller Part II

}
7.4. OUTPUT DEVICES 207
//*************************************************************************
//performs specified LCD related command
//*************************************************************************
void putcommand(unsigned char˜(d)
{
DDRC = 0xff; //set PORTC as output
DDRD = DDRD|0xC0; //make PORTD[7:6] output
PORTD = PORTD&0x7f; //RS=0
PORTC = d;
PORTD = PORTD|0x40; //E=1
PORTD = PORTD&0xbf; //E=0
delay_5ms();
}
//*************************************************************************
7.4.7 GRAPHIC LIQUID CRYSTAL DISPLAY (GLCD)
A graphic LCD may be used to generate custom displays. A display is assembled as a collection of
picture elements (pixels). The pixels may be pre-arranged into specific graphic representations such
as geometric shapes, fonts, or any custom image feature. In this section, we illustrate how to interface
a graphic LCD to the ATmega164 and also how to program a specific pixel location on the GLCD.
We employ the Hantronix HDM64GS12L-4 128 × 64 pixel graphics LCD display module as a
representative sample of this type of display. Figures and sample code in this section were adapted
from Hantronix literature and also sample GLCD code (Hantronix).
Interfacing a GLCD is similar to interfacing a character LCD. A number of control signals
are required to control the action of the GLCD. We will use PORTD[5:0] of the ATmega164 to
generate the control signals required by the GLCD. We employ PORTC of the ATmega164 to send
data or instructions to the GLCD. The interface is illustrated in Figure 7.14. The definitions for
each of the control signals are provided in Figure 7.15 along with the necessary timing signals and
pin definitions for the GLCD.
The GLCD consists of two separate display areas designated left and right. Each display
area is divided into eight horizontal pages designated page 1 through page 8. Each page consists
of 64 × 8 bits of RAM memory. The left page is organized into 64 columns, (1 through 64) in the
y direction and 64 segments (1 through 64) in the x direction. The right page is organized into
64 columns, (1 through 64) in the y direction and 64 segments (65 through 128) in the x direction.
This organization is shown in Figure 7.15.