Pramod,

Perhaps i do not understand you question correctly.

Connecting an LCD, i8255, or E2ROM, as you know, requires only accomodating the signalling required for interface.

If your question is how do you interface all three of the above simulataneously to an 8051, you must decode each uniquely. This decode can be done simply by using the Most Significant Address Bits. The decoder is simple and readily implemented in discrete gates, PLD, etc...

However, If you Port pin utilization is low you might just use availiable port pins to enable the individual devices, avoiding an external decoder.

A mixed implementation is also possible where the LCD implements using a dedicated port for data, some other port pins for exchange signalling, and say the E2ROM being connected (solely) to the Memory Bus Signalling (being selected for any external memory cycle).

If the LCD (or other device) is Port interfaced, you will use:

Port mov's and setb/clrb to implement the signal exchange. Simultaneously (assuming a memory mapped peripheral) you would employ movx instructions to access the memory mapped peripheral. In this case (assuming no other decode exists) the individual memory mapped peripheral will "ghost" through out the memory address range.

In hope this remotely addresses you question.

regards,
p