Hi,
Thank you Mr.Cooper and Mr.Neil, the link you sent was very informative.

Mr.Waclawek, I tried out your "my quick test is:" and worked wonders, the bootloader gave the exact output as you had depicted.

I have come across another hurdle and the problem statement is as below:

Blinking an LED connected to P3.7: The code was written in C51 and compiled by Keil uV3. The hex lump is:

:10000300E4FDFCC3ED9FEC9E5015E4FBFA0BBB0033
:0F001300010ABA03F8BBC5F50DBD00010C80E46E
:0100220022BB
:0E002300C2B77FC87E00120003D2B7020003EE
:03000000020031CA
:0C003100787FE4F6D8FD758107020023FB
:00000001FF

The code was first burnt using Flash Magic and it worked.
Then I sent the same hex lump with a serial communication tool developed in VC++ and the bootloader echoed each record with a '.'. The echoed lump is:

:10000300E4FDFCC3ED9FEC9E5015E4FBFA0BBB0033.

:0F001300010ABA03F8BBC5F50DBD00010C80E46E.

:0100220022BB.

:0E002300C2B77FC87E00120003D2B7020003EE.

:03000000020031CA.

:0C003100787FE4F6D8FD758107020023FB.

:00000001FF.

The code worked as expected.

Then I changed the code to blink an LED connected to P3.6, directly burnt the code using the VC++ tool and the code worked as expected but the problem was when I tried to burn the first code back into the controller using the VC++ tool. The echoed lump is:

:10000300E4FDFCC3ED9FEC9E5015E4FBFA0BBB0033.

:0F001300010ABA03F8BBC5F50DBD00010C80E46E.

:0100220022BB.

:0E002300C2B77FC87E00120003D2B7020003EER

:03000000020031CA.

:0C003100787FE4F6D8FD758107020023FB.

:00000001FF.

Please note the 'R' in the fourth record set. I understand that the bootloader sends an 'R' if the record was not burnt properly so what could be the problem?

Note: Burnt the same hex using Flash Magic and it works fine.