serial read and output to dmd with scrolling message

Hello,
I have use the arduino mega 2560 and p10 module, i have send 104 bytes serially and output to dmd working done .

font - 5x7
p10 module -10

i have arrange 4 line of 26 bytes(26*4=104)

now my question is how to scroll message of last line(ie. bytes from 79 to 104)

my code is below for serial read

/read serial data and displyed on dmd diaplay/

#include <DMD.h>
#include <SPI.h>
#include <TimerOne.h>
#include “SystemFont5x7.h”
#include “Arial_black_16.h”
#define DISPLAYS_ACROSS 10
#define DISPLAYS_DOWN 1
DMD dmd(DISPLAYS_ACROSS, DISPLAYS_DOWN);

const int SerialBufferSize = 104;
char serIn[SerialBufferSize+1];

void ScanDMD()
{
dmd.scanDisplayBySPI();
}
void setup()
{
Timer1.initialize( 3000 );
Timer1.attachInterrupt( ScanDMD );
dmd.clearScreen( true );

Serial.begin(9600);
}

void loop()
{

if (Serial.available())
{
int chars_in = 0;

// void serialFlush(){
while (Serial.available() > 0 && chars_in < SerialBufferSize)
{
serIn[chars_in] = Serial.read();
Serial.write( byte(serIn[chars_in]));

chars_in++;

}

}

dmd.selectFont(SystemFont5x7);

dmd.drawString(0, 0, serIn,26, GRAPHICS_NORMAL );
dmd.drawString(0, 8, serIn+26,26,GRAPHICS_NORMAL);
dmd.drawString(160, 0, serIn+52, 26, GRAPHICS_NORMAL );
dmd.drawString(160, 8, serIn+78, 26, GRAPHICS_NORMAL );

delay(1000);

}

how to write code for scroll bytes from 79 to 104

please help and send the code for it.