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Microcontroladores 8051

2.3. Special function registers (SFR) for 8051 microcontrollers

The registration area or special functions (SFR) is between 80H and FFH address the internal memory of the microcontroller.

This memory area can not be used as data memory, it is clear that if we write out of control in the memory allocated to a special register, modify the behavior of the microcontroller, resulting in unexpected results as the affected record. Although the memory locations that are not assigned to a special register can be used to hold data, it is not advisable to use, it has to bear in mind that these may be reserved and assigned to special registers in other models or manufacturers of microcontrollers and our program will conflict when changing model.

The input and output ports also occupy a specific position or memory addresses. The memory locations on the left side (80h, 88h, 90H ..) are reserved for routing bit so that the concerned records may be accessed via this system.

The following table shows the layout of each record in 8051 and 8052 microcontroller.

F8H FFH
F0H B *
F7H
E8H EFH
E0h ACC *
E7H
D8H DFH
D0H PSW *
D7H
C8H T2CON * #
RCAP2L #
RCAP2H #
TL2 #
TH2 #
CFH
C0h C7H
B8H IP *
BFH
B0h P3 *
B7H
A8h IE *
AFH
A0H P2 *
A7H
98H SCON *
SBUF 9FH
90H P1 *
97H
88h TCON *
TMOD TL0 TL1 TH0 TH1 8FH
80H P0 *
SP DPL DPH PCON 87H

The following table shows the description and the symbols of each bit or pin of the internal registers (SFR) of the 8051/8052 microcontroller family.

Register Description Address Command bit or alternate function port Reset value
MSB LSB
ACC * Accumulator
(Accumulator)
E0h E7 E6 E5 E4 E3 E2 E1 E0 00H
B * Register B
(Register B)
F0H F7 F6 F5 F4 F3 F2 F1 F0 00H
DPTR: Data Pointer
(Data Pointer) (2 bytes)
DPH High byte of DPTR
(Data pointer high)
83H 00H
DPL Low byte of DPTR
(Data pointer low)
82H 00H
AF AE AD AC AB AA A9 A8
IE * Enable interrupts
(Interrupt enable)
A8h EA - ET2 ES ET1 EX1 ET0 EX0 0x000000B
BF BE BD BC BB BA B9 B8
IP * Priority interrupts
(Interrupt priority)
B8H - - PT2 PS PT1 PX1 PT0 PX0 0x000000B
87 86 85 84 83 82 81 80
P0 * Port 0 (Port 0) 80H AD7 AD6 AD5 AD4 AD3 AD2 AD1 AD0 FFH
97 96 95 94 93 92 91 90
P1 * Port 1 (Port 1) 90H - - - - - - T2EX T2 FFH
A7 A6 A5 A4 A3 A2 A1 A0
P2 * Port 2 (Port 2) A0H A15 A14 A13 A12 A11 A10 A9 A8 FFH
B7 B6 B5 B4 B3 B2 B1 B0
P3 * Port 3 (Port 3) B0h RD WR T1 T0 INT1 INT0 TxD RxD FFH
PCON1 Consumption control
(Power control)
87H SMOD - - - GF1 GF0 PD IDL 0xxxxxxxB
D7 D6 D5 D4 D3 D2 D1 D0
PSW * Program status word
(Program status word)
D0H CY AC F0 RS1 RS0 OV - P 00H

Register Description Address Bit command or alternate function port Reset value
MSB LSB
RCAP2H # Capture high byte
(Capture high)
CBH 00H
RCAPL # Capture Low byte
(Capture low)
CAH 00H
SBUF Serial Data Buffer
(Serial data buffer)
99h xxxxxxxxB
9F 9E 9D 9C 9B 9A 99 98
SCON * Serial Port Control
(Serial controller)
98H SM0 SM1 SM2 REN TB8 Rb8 IT RI 00H
SP Stack pointer
(Stack Pointer)
81F 07H
8F 8E 8D 8C 8B 8A 89 88
TCON * Control Timers
(Timer Control)
88h TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 00H
CF CE CD CC CB CA C9 C8
T2CON * # Timer 2 Control
(Timer 2 contro l)
C8H TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2 CP/RL2 00H
TH0 Timer 0 upper
(Timer high 0)
8CH 00H
TH1 Timer 1 upper
(Timer high 1)
8DH 00H
TH2 # Timer 2 top
(Timer high 2)
CDH 00H
TL0 Timer 0 lower
(Timer Low 0)
8AH 00H
TL1 Timer 1 lower
(Timer Low 1)
8BH 00H
TL2 # Timer 2 lower
(Timer Low 2)
CCH 00H
TMOD Timers Mode
(Timer mode)
89h GATE C / T M1 M0 GATE C / T M1 M0 00H

* Register with bit-level addressing.
# Records added in the 8052 microcontroller family.

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