8051 Micro controller is 8-bit controller.it contain 128Byte of internal RAM.internal RAM divided into three section.
- 32 bytes-Register Bank.
- 16 Byte-bit addressable area.
- 80 byte-Scratch pad area & SFR.
below diagram show architecture of RAM
32 Byte-Register Bank
there are four register bank into RAM.each register bank contain 8 registers of 1byte.so total 32 register in register bank.by default register bank 0 is selected.to change the register bank we have to set value of two register selection bit in PSW register.
In RAM there are 16 byte area in which 128 bit we can accessed by suitable instruction.the address range of bits addressable area is 00h (LSB of first byte of 20h ) to 7Fh(MSB of last byte if 2Fh).
remaining 80 bytes are general purpose area which are shared with DATA and SFR (special function register)upper 128 byte of RAM accessed indirect addressing while SFR accessed by direct addressing only.SFR contain special register like ACC,B,IE,IP,IE etc.below diagram show memory allocation for SFR.
