9.0 Special Function Registers (SFRs)
Special Function Registers (SFRs) are the primary software interface for controlling and monitoring the 8051’s peripherals and core functions. They occupy a specific address space within the internal data memory map and can be accessed by name or by direct address.
9.2 SFR Address Map
SFRs occupy the upper 128 bytes of the internal data memory space, from address 80H to FFH. Many of these registers are bit-addressable, allowing for fine-grained control of individual flags and configuration bits.
| Byte Address | Bit Addressable SFRs |
| FFH | |
| F0H | B (F7 … F0) |
| EFH | |
| E0H | ACC (E7 … E0) |
| DFH | |
| D0H | PSW (D7 … D0) |
| CFH | |
| C8H | |
| BFH | |
| B8H | IP (BC … B8) |
| B7H | |
| B0H | P3 (B7 … B0) |
| AFH | |
| A8H | IE (AF … A8) |
| A7H | |
| A0H | P2 (A7 … A0) |
| 9FH | |
| 99H | SBUF (Not bit Addressable) |
| 98H | SCON (9F … 98) |
| 97H | |
| 90H | P1 (97 … 90) |
| 8FH | |
| 8DH | TH1 (Not bit Addressable) |
| 8CH | TH0 (Not bit Addressable) |
| 8BH | TL1 (Not bit Addressable) |
| 8AH | TL0 (Not bit Addressable) |
| 89H | TMOD (Not bit Addressable) |
| 88H | TCON (8F … 88) |
| 87H | PCON (Not bit Addressable) |
| 83H | DPH (Not bit Addressable) |
| 82H | DPL (Not bit Addressable) |
| 81H | SP (Not bit Addressable) |
| 80H | P0 (87 … 80) |
This software interface is complemented by the physical hardware pins required for fundamental system operation.