MICROPROCESSOR AND MICROCONTROLLER

Detailed explanation-1: -Although the address range of 80H through FFH offers 128 possible addresses, there are only 21 SFRs in a standard 8051. The Accumulator or Register A is the most important and most used 8051 Microcontroller SFRs.

Detailed explanation-2: -The Intel 80196 class microcontroller has 24 SFRs, each 1 Byte in size; standard Intel 8051 chips have 21 SFRs. The Special Function Register (SFR) is the upper area of addressable memory, from address 0x80 to 0xFF.

Detailed explanation-3: -In the 8051, register A, B, DPTR, and PSW are a part of the group of registers commonly referred to as SFR (special function registers). An SFR can be accessed by its name or by its address.

Detailed explanation-4: -There are 21 unique location for these 21 special function registers and each of these registers is of 1 byte size some of these special function register are bit addressable (which means you can access and individual bits inside a single byte) other are only byte addressable.