Special Function Registers (SFRs) in 8051

SFRs occupy internal RAM 80H–FFH (only addresses ending 0H/8H bit-addressable, total 21-26 SFRs). Key SFRs:

SFR	Address	Purpose
ACC (A)	E0H	Accumulator, ALU results
B	F0H	Multiply/divide, storage
PSW	D0H	Flags: CY, AC, FO, RS1,RS0, OV, P
SP	81H	Stack Pointer
DPL/DPH	82H/83H	Data Pointer 16-bit for external access
P0-P3	80H,90H,A0H,B0H	I/O ports
IE	A8H	Interrupt Enable (EA, ES, ET1,EX1,ET0,EX0)
IP	B8H	Interrupt Priority
TCON	88H	Timer control (TF1,TR1,TF0,TR0,IE1,IT1,IE0,IT0)
TMOD	89H	Timer mode (GATE,C/T,M1,M0)
TH0/TL0, TH1/TL1	8AH-8DH	Timer counts
SCON	98H	Serial control (SM0,SM1,SM2,REN,TB8,RB8,TI,RI)
SBUF	99H	Serial buffer (TX/RX)
PCON	87H	Power control (SMOD, IDL, PD)

Bit-addressable SFRs (marked *) allow SETB/CLR. Maps allow direct bit manipulation for control. Example: SETB TR1 starts Timer1; JNB TF0 loop etc.