AN-908: Interfacing the HD44780-Based Character LCD to an ADuC702x (Rev. 0)

AN-908
APPLICATION NOTE
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Interfacing the HD44780-Based Character LCD to an ADuC702x
MicroConverter ADuC702x Development System
INTRODUCTION
A vast array of LCD displays are currently available and, fortunately, many of these LCDs comply with the HD44780U
standard. This standard refers to the LCD controller chip,
which accepts data from the ADuC702x and communicates
with the LCD screen. HD44780 standard LCD screens are
available in numerous formats, the most popular of which are
the 16 × 2 and 20 × 2 formats. This application note describes
the commands to control the basic functions of the LCD.
Register Select Line (RS)
INTERFACING WITH AN HD44780 LCD
When this line is low, the information on the data bus is
written to the LCD controller. If this line is high, the LCD
controller can be read. This is used to check the status of
the LCD.
This line indicates to the LCD controller whether to treat the
data byte as a command or as text data to be displayed on the
screen. If the RS line is high, the data byte is treated as text to
be displayed; if the RS line is low, the data byte is treated as a
command.
Read/Write Line (R/W)
The data bus that connects the HD44780 to the MicroConveter®
can be 8 or 4 bits wide; in this application note, only the case of
an 8-bit data bus is examined. In addition to the data bus, three
control lines are required; thus, a total of 11 pins are required to
interface the LCD to the MicroConverter.
As shown in Figure 1, the eight data lines connect to Port 1 of
the MicroConverter, and the three control lines connect to
Port 0.5, Port 0.7, and Port 2.0.
The eight data lines that form the data bus, are referred to as
DB0, and DB1 through DB7.
The source code used to define this interface is given as follows:
The three control lines are referred to as EN, RS and R/W.
Their functions are as follows:
unsigned char Init_MC08_LCD()
Enable Line (EN)
GP0DAT = 0xA0000000;
// P0.5 = RS, EN = P0.7
This line indicates the start of a transmission of a data byte to
the LCD controller. To indicate the start of transmission, this
line is brought high; when transmission is complete, the EN line
is brought low indicating that the transmission is complete.
GP1DAT = 0xFF000000;
// P1.[7:0] = DB[0:7]
GP2DAT = 0x01000000;
// P2.0 = R/W
{
return 0x1;
}
DB0
P1.1
DB1
P1.2
DB2
P1.3
DB3
P1.4
DB4
P1.5
DB5
P1.6
DB6
P1.7
DB7
P0.7
EN
P0.5
RS
P2.0
3.3V
HD44780
R/W
VO
VDD
VSS
Figure 1. Connecting an HD44780 LCD to an ADuC702x
Rev. 0 | Page 1 of 8
06695-001
ADuC702x
P1.0
AN-908
TABLE OF CONTENTS
Introduction ...................................................................................... 1
Setting the Entry Mode.....................................................................5
Interfacing with an HD44780 LCD................................................ 1
Writing Text to the LCD Screen ......................................................6
Configuring the LCD Screen .......................................................... 3
Notes and References ........................................................................7
Clearing the LCD Screen ................................................................. 4
Rev. 0 | Page 2 of 8
AN-908
CONFIGURING THE LCD SCREEN
To display text to the LCD screen, the LCD screen must be
configured first. The configuration defines to the LCD controller the type of LCD screen that is being used, as well as
the data bus format and font. The various commands available
are listed in detail in any data sheet for an HD44780U-based
LCD module.
In the example that follows, the LCD is configured to use an
8-bit data bus and display in a 5 × 7 dot character font. This
configuration is achieved by sending 0x38 to the LCD controller
through the Select_Function_Set function.
unsigned char Select_Function_Set(unsigned char ucFunctionSet)
{
unsigned long ulFunction = 0;
delay (10000);
RdStatus = ReadStatus();
ulFunction = ucFunctionSet;
ulFunction = (ulFunction << 16);
ulFunction |= 0xFF000000;
GP0DAT = 0xA0000000;
//Clear RS pin(P0.5), clear E pin (P0.7) = R/W)
GP2DAT = 0x01000000;
//Clear R/W pin
(P2.0 = R/W)
delay (5);
GP0SET = 0x800000;
// Set E high
delay (5);
// Allow min 800 ns setup time
GP1DAT = ulFunction;
// Write to register
delay (5);
// allow hold time of 500 ns min
GP0CLR = 0x800000;
// Set E low
delay (5);
return 0x1;
}
The ReadStatus function is used to read the busy signal output from the HD44780 module.
Rev. 0 | Page 3 of 8
AN-908
CLEARING THE LCD SCREEN
Before writing to the screen, it must first be cleared. To do this, use the function, Clear_Display_LCD, as outlined in the following:
unsigned char Clear_Display_LCD(unsigned char ucFunctionSet)
{
unsigned long ulFunction = 0;
delay (10000);
RdStatus = ReadStatus();
ulFunction = ucFunctionSet;
ulFunction = (ulFunction << 16);
ulFunction |= 0xFF000000;
GP0DAT = 0xA0000000;
//Clear RS pin(P0.5), clear E pin (P0.7) = R/W)
GP2DAT = 0x01000000;
//Clear R/W pin
(P2.0 = R/W)
delay (5);
GP0SET = 0x800000;
// Set E high
delay (5);
// Allow min 800 ns setup time
GP1DAT = ulFunction;
// Write to register
delay (5);
// Allow hold time of 500 ns min
GP0CLR = 0x800000;
// Set E low
delay (2000);
// Minimum clear time of 1.58 ms
return 0x1;
}
Rev. 0 | Page 4 of 8
AN-908
SETTING THE ENTRY MODE
The entry mode must also be set. For this example, the increment is on and there is no shifting. This is achieved by sending 0x6 to the
LCD controller through the Set_Entry_Mode function, as follows:
unsigned char Set_Entry_Mode(unsigned char ucFunctionSet)
{
unsigned long ulFunction = 0;
delay (10000);
RdStatus = ReadStatus();
ulFunction = ucFunctionSet;
ulFunction = (ulFunction << 16);
ulFunction |= 0xFF000000;
GP0DAT = 0xA0000000;
//Clear RS pin(P0.5), clear E pin (P0.7) = R/W)
GP2DAT = 0x01000000;
//Clear R/W pin
(P2.0 = R/W)
delay (5);
GP0SET = 0x800000;
// Set E high
delay (5);
// Allow min 800 ns setup time
GP1DAT = ulFunction;
// Write to register
delay (5);
// Allow hold time of 500 ns min
GP0CLR = 0x800000;
// Set E low
delay (5);
return 0x1;
}
Rev. 0 | Page 5 of 8
AN-908
WRITING TEXT TO THE LCD SCREEN
In the sample program, the following text is written to the LCD screen:
Analog Devices
ADuC7020 LCDdemo
To do this, use the Wr_Data_LCD function, after the screen is cleared.
For example, to output the Character A, use its hexadecimal representation, 0x41. All other characters must be represented in their
hexadecimal forms and sent to the function to be processed as follows:
unsigned char Wr_Data_LCD(unsigned char ucFunctionSet)
{
unsigned long ulFunction = 0;
delay (10000);
RdStatus = ReadStatus();
ulFunction = ucFunctionSet;
ulFunction = (ulFunction << 16);
ulFunction |= 0xFF000000;
GP0DAT = 0xA0200000;
//Set RS pin(P0.5), clear E pin (P0.7) = R/W)
GP2DAT = 0x01000000;
//Clear R/W pin
(P2.0 = R/W)
delay (5);
GP0SET = 0x800000;
// Set E high
delay (5);
// Allow min 800 ns setup time
GP1DAT = ulFunction;
// Write to register
delay (5);
// Allow hold time of 500 ns min
GP0CLR = 0x800000;
// Set E low
delay (5);
GP0CLR = 0x200000;
// Set RS low
return 0x1;
}
Rev. 0 | Page 6 of 8
AN-908
NOTES AND REFERENCES
The dot matrix LCD screen used in implementation of all the
processes described in this application note was the Samsung
S6A0070 driver and controller. See the Samsung website for
more information on their products.
Table 1. Analog Devices ADuC702x Series
For information on specific Analog Devices, Inc. products in
the ADuC702x family, select from among the products listed in
Table 1.
Part No.
ADuC7020
ADuC7021
ADuC7022
ADuC7024
ADuC7025
ADuC7026
ADuC7027
ADuC7028
Rev. 0 | Page 7 of 8
No.
GPIO
Pins
14
13
13
30
30
40
40
40
No. ADC
Channels
5
8
10
10
12
12
16
16
No. 12-Bit
DAC Outputs
4
2
N/A
2
N/A
4
N/A
4
Temp.
Range (°C)
−40 to +105
−40 to +85
−40 to +85
−40 to +105
−40 to +105
−40 to +125
−40 to +125
−40 to +125
AN-908
NOTES
©2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
AN06695-0-6/07(0)
Rev. 0 | Page 8 of 8
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