8051 REGISTERS

On-Chip MemoryInternal RAM

Registers

0706050403020100

R7R6R5R4R3R2R1R0

0F

08

17

10

1F

18

Bank 3

Bank 2

Bank 1

Bank 0

Four Register BanksEach bank has R0-R7Selectable by psw.2,3

Bit Addressable Memory

20h – 2Fh (16 locations X 8-bits = 128 bits)

7F 78

1A

10

0F 08

07 06 05 04 03 02 01 00

27

26

25

24

23

22

21

20

2F

2E

2D

2C

2B

2A

29

28

Special Function Registers

DATA registers

CONTROL registersTimersSerial portsInterrupt systemAnalog to Digital converterDigital to Analog converterEtc.

Addresses 80h – FFhDirect Addressing used to access SFRs

A (Accumulator)BPSW (Program Status Word)SP (Stack Pointer)PC (Program Counter)DPTR (Data Pointer)

8051 CPU Registers

Used in assembler instructions

A

B

R0

R1

R3

R4

R2

R5

R7

R6

DPH DPL

PC

DPTR

PC

Some 8051 16-bit Register

Some 8-bit Registers of the

8051

PROGRAM STATUS WORD

IE: Interrupt Enable Register(bit addressable)

• If the bit is 0, the corresponding interrupt is disabled. Otherwise, the interrupt is enabled.

IP: Interrupt Priority Register(bit addressable)

• If the bit is 0, the corresponding interrupt has a lower priority and if the bit is 1, the interrupt has a higher priority

TCON: Timer/Counter Control Register (bit addressable)

TMOD: Timer/Counter Mode Control Register (not bit addressable)

PCON – Power Control Register

Address: 87H (not bit addressable) SMOD – Serial mode bit used to determine the baud rate with Timer 1. GF1 and GF0 are General purpose flags not implemented on the standard device PD is the power down bit. Not implemented on the standard device IDL activate the idle mode to save power. Not implemented on the standard device