From the tutorial on this web:

"While DPTR is most often used to point to data in external memory, many programmers often take advantge of the fact that it’s the only true 16-bit register available. It is often used to store 2-byte values which have nothing to do with memory locations."

In the instruction set on this web:

MOVC A,@A+DPTR

Further i found the following from a book:

"Two data transfer instructions are available for reading lookup tables in program memmory. MOVC uses either program counter or the data pointer as the base register and accummulator as the offset."

My point is , Set bit, CLR bit, CPL bit instructions are avaiable for sending data out from 8051 but iam scanning a port lets say port 0 and in that wanna find out how can a lookup table be use to find out whether a bit of Port 0 is set high by an extrenal source ? CJNE & Acc can be used but i guess lookup table are more effective.

Want to learn how the lookup table can be use to scan a port and what actually happens when a lookup table DPTR and Define Byte DB are used together for scanning a port.