architecture of 8051 controller

fig:block diagram of 8051   

micro controller is single chip on which timer,counter,serial port,I/O ports,oscillator,memory in built.Intel was found 8051 micro controller in 1981 with in built memory in 8051 micro controller 4KB ROM,128byte RAM,2 timer/counter,crystal oscillator,4 I/O ports are inbuilt.the 8051 family controller is eight bit with 40 pins IC.

 

feature:

• eight bit CPU each register A and B.
• PC(program counter) and DPTR (data pointer) are two sixteen bit register.
• eight bit program status word (PSW) register and stack pointer(SP).
• 4KB internal ROM and 128Bytes internal RAM.
• 32 inputs/outputs pins divided in four ports(P0-P1).
• two 16 bit timer/counter:T0,T1
• full duplex serial ports.
• control register:TCON,SCON,TMOD,IP,IE.
• five interrupt source.
• oscillator and clock circuit.
• support power down and idle mode for power saving.

FUNCTION OF EACH BLOCK OF 8051
ALU:

• it arithmetic and logic units.
• used to perform arithmetic and logical operation.

REGISTER A:

• its call accumulator.
• its used as destination in all arithmetic and logical instruction.
• its also used in data transfer between 8051 and external memory.

REGISTER B:

• its used with A in multiplication and division instruction.

PC(program counter):

• its 16 bit register.
• its used to store address of next instruction to be executed.

DPTR(data pointer):

• its also 16 bit register.
• used to store 16 bit data.
• also store 16 bit address of external memory.

STACK POINTER(SP):

• its 8 bit register.
• store address of top of stack.
• stack is part of RAM where data store temporary.

PSW(program status word):

• its 8 bit register.
• its contain flag register which are change after arithmetic and logical instruction.
• its contain carry,auxiliary carry,parity,overflow and user define  flags.
• also contain register bank selection bits.

INTERNAL MEMORY:

• internal RAM is 128 byte and ROM is 4KB called program memory.
• internal RAM divided in 3 parts.

1.     32 bytes for register bank(four register bank each contain 8 register of 1 byte)(00-1Fh)
2.     16 bit addressable area where u can access individual bit(20-2Fh)
3.     80 byte for scratch pad area(30-7Fh).

EXTERNAL MEMORY:

• we connect 64KB of external memory with 8051.

SPECIAL FUNCTION REGISTER(SFR):

• IP,IE are used for interrupt.
• TCON,TMOD used for timer/counter operation.
• SCON for serial communication.
• PCON for power saving modes.

I/O PORTS:

• there are 32 pins for input and outputs.
• in 8051 four I/O ports each contain 8 pins.
• PORT 0:its provide 8 bit data as well as lower byte address(AD0-AD7).
• PORT 1:it for input/output.
• PORT 2:its provide higher byte of address.
• PORT 3:its input/output ports as well as some alternative function provide.

OSCILLATOR:

• its connected between XTAL1 and XTAL2 pins.
• its generated clock pulse for controller.

ALE/PROG:

• its demultiplex address and data bus which are multiplex(AD0-AD7).
• initial ALE high so work as address bus then ALE become LOW so work as data bus.

PSEN:

• its output pin.
• which indicate program run from internal or external memory.
• if high then program executing from external memory otherwise internal memory.

EA:

• its input pin.
• when using internal memory this connected with Vcc.
• its connected to ground when used external memory.

RST:

• its input pin and active high pins.
• to restart micro controller we have to push this for at least two machine cycles.