Abstract: This application note describes how a DS2408 1-Wire 8-Channel Addressable Switch can be used to display characters on an LCD. The code is written using the 1-Wire API for Java. A diagram shows how to hook the DS2408 to any LCD using a Hitachi-44780-based LCD controller chip.
General Overview
This application note demonstrates creating a 1-Wire® 8-bit LCD. The code to drive the DS2408 LCD display is also provided. The LCD used was the Data Vision Model NO: DV-16252-S1FBLY, however any LCD with this Hitachi 44780 based LCD controller chip can be used.
For Larger Image
Figure 1. 1-Wire LCD schematic.
Main Display Program
The code examples provided are written using the 1-Wire API for Java (http://www.ibutton.com/software/1wire/1wire_api.html). The main program, displayed in Figure 2, accesses the default adapter to talk to the DS2408 and initializes the LCD. Depending on the size of the LCD used the numCharsPerLine, secondStart and thirdStart may need to be updated. The fixed string '0123456789' is printed out to the LCD in the loop after the initialization is complete.
Figure 2. 1-Wire LCD main example code
import com.dalsemi.onewire.*;
import com.dalsemi.onewire.adapter.*;
import com.dalsemi.onewire.container.*;
import com.dalsemi.onewire.utils.*;
public class DisplayLCD
{
static DSPortAdapter adapter;
static byte[] address29 = new byte[]{0,0,0,0,0,0,0,0};
static OneWireContainer29 owc29;
public static void main(String[] args)
throws Exception
{
adapter = OneWireAccessProvider.getDefaultAdapter();
adapter.targetFamily(0x29);
if(!adapter.findFirstDevice())
return;
owc29 = (OneWireContainer29)adapter.getFirstDeviceContainer();
address29 = owc29.getAddress();
System.out.println("Initing");
doOverdrive();
fixResetMode();
initLCD();
System.out.println("Done Initing");
byte[] chars = "0123456789".getBytes();
int i = 0;
int numCharsPerLine = 20;
int secondStart = numCharsPerLine - chars.length;
int thirdStart = chars.length - secondStart;
while(true)
{
System.out.print(".");
returnHome();
writeChars(chars, i, chars.length - i);
if(i>thirdStart)
{
writeChars(chars, 0, chars.length);
writeChars(chars, 0, i - thirdStart);
}
else
{
writeChars(chars, 0, secondStart + i);
}
i = (i+1)%chars.length;
}
}
}
Figure 3. Initializing LCD example code
public static void initLCD()
{
setLatchOutput(0x30);
waitMS(100);
// init
setLatchOutput(0x38);
waitMS(10);
// Enable Display, Cursor, and Blinking
setLatchOutput(0x0F);
// Entry-mode: auto-increment, no shift
setLatchOutput(0x06);
clearDisplay();
}
Initializing LCD
In Figure 3, the code to initial the Data Vision Model NO: DV-16252-S1FBLY is shown. This will change depending on the model of LCD being used.
Setting RSTZ Pin Mode Control
In Figure 4, the RSTZ pin is being configured to the STRB output mode. This is connected to the LCD enable signal for writing.
Figure 4. Setting RSTZ pin example code
public static void fixResetMode()
{
try
{
adapter.beginExclusive(true);
byte[] register = owc29.readRegister();
owc29.setResetMode(register, false);
owc29.writeRegister(register);
}
catch(Exception e)
{;}
finally
{
adapter.endExclusive();
}
}
Display Characters on LCD
In Figure 5, the code to display the characters to the LCD is provided. The DS2408's P7 is being used to select whether text or commands are being sent. The method setLatchOutput is sending the data through P0-P6 of the DS2408.
Figure 5. Display characters on LCD example code
public static void writeString(String message)
throws Exception
{
byte[] chars = message.getBytes();
writeChars(chars, 0, chars.length);
}
public static void writeChars(byte[] bytesToWrite, int offset, int length)
{
length += offset;
for(int i=offset; i<length; i++)
{
if((bytesToWrite[i]&0x80)==0x080)
{
System.out.println("Unprintable character: " + (char)bytesToWrite[i]);
}
else
{
setLatchOutput(bytesToWrite[i]|0x80);
}
}
}
private static void setLatchOutput(int output)
{
try
{
adapter.beginExclusive(true);
adapter.assertSelect(address29);
byte[] buffer = new byte[5];
// channel access write command
buffer[0] = 0x5A;
buffer[1] = (byte)output;
buffer[2] = (byte)(~output);
buffer[3] = (byte)0x0FF;
buffer[4] = (byte)0x0FF;
adapter.dataBlock(buffer, 0, 5);
}
catch(Exception e)
{;}
finally
{
adapter.endExclusive();
}
}
Clearing and Positioning
In Figure 6, the methods for clearing the LCD and positioning the cursor in the starting position are shown.
Figure 6. Clearing and positioning
public static void returnHome()
{
setLatchOutput(0x02);
waitMS(2);
}
public static void clearDisplay()
{
// Clear Display
setLatchOutput(0x01);
waitMS(2);
}
Additional Resource Methods
In Figure 7, additional resource methods that were used are displayed.
Figure 7. Resource methods
public static void doOverdrive()
{
try
{
adapter.reset();
adapter.setSpeed(adapter.SPEED_REGULAR);
adapter.reset();
adapter.putByte(0x3C); //overdrive skip rom
adapter.setSpeed(adapter.SPEED_OVERDRIVE);
}
catch(Exception e)
{;}
}
public static void waitMS(long timeToWait)
{
try
{
Thread.sleep(timeToWait);
}
catch(InterruptedException ie)
{;}
}
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APP 3286: Aug 24, 2004
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AN3286,
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