Hi Sarathi,
I'm pleased you found the HC(S)08 products. The HC08 has been very successful in automotive markets, and products such as the newly announced MC9S08Dx family will prove to be popular in this market, too.
About the ADC, X - add with carry, indexed addressing mode. It doesn't work in the way that you think. In this mode, the H:X register acts as an index to the operand, so if H:X contains 0x0800, then the Add with Carry uses the value pointed to at address 0x0800. It just takes 3 cycles. First cycle is R - Read, second cycle is Free, 3rd cycle is P - program access.
You should look at the Addressing Mode section of the Core Reference Manual HCS08RMV1.pdf