Hi Gopal,

This idea to begin from 0H needs to be given more thought than you think. And maybe its time to open the 8051_Bible !! I think there was a discussion on this some time back ( sorry I could not locate it ) The status of SFRs are important in deciding to start from 0H by jumping there.

There are many fine differences in each method of starting :

1. Power on Reset - the mother of all Resets. All SFRs initialized, Power On Flag ( if applicable) set and start execution from 0H. If you are using this POF, then a power down and up is the only way to make the on chip hardware to set it. After that you can set/clear this bit in software.

2. Idle mode - Invoked by software and exited by any enabled interrupt or Reset. Here your IRAM and SFRs recover as when entering idle mode.

3. Power Down mode - Invoked by software and exited only by Reset or External Interrupt. IRAM contents recover but SFRs are initialized in the first case but both are recovered in the second case.

4. WDT reset - This, as Joseph already mentioned, is a good way and maybe the only way to start fresh. But even here the POF bit is not reset. ( Based on my understanding in the 89c51rd2 data sheet )

So you will have to analyse the matter in detail before planning to jump to 0H. Or better still choose a MCU that CAN be reset by software.

Raghu