B.Suresh Asst professor ECE Department Pointer(SP): It is 8-bit wide. it will reside any where in...

8051 Microcontroller

B.Suresh

Asst professor

ECE Department

B.Suresh, Asst.prof ,ECE Department,ASIST,Paritala

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8051 Microcontroller


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Features of 8051 Microcontroller

It is a 8-bit Microcontroller

It is a 40 pin chip available in DIP package

It has 8-bit 4 parallel ports

It contains internal RAM 128 Bytes and internal 4KB ROM

It has 128 user defined flags

Its maximum internal clock frequency rating is 12MHz


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40

39

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31

P1.0

P1.1

P1.2

P1.3

P1.4

P1.5

P1.6

RST

(RXD) P3.0

(TXD) P3.1

(INT0) P3.2

(INT1) P3.3

(T0) P3.4

(T1) P3.5

(WR) P3.6

XTAL 2

XTAL 1

GND

Vcc

P0.0(AD0)

P2.0(A8)

P2.1(A9)

P2.2(A10)

P2.3(A11)

P2.4(A12)

P2.5(A13)

P2.6(A14)

P2.7(A15)

PSEN

ALE/PROG

EA/VPP

P0.6(AD6)

P0.7(AD7)

P0.5(AD5)

P0.4(AD4)

P0.3(AD3)

P0.2(AD2)

P0.1(AD1)

(RD) P3.7

P1.7

(Serial)

interrupt

Timer

Ex M W/R

clock

Ext

Memory

Address

Ext Memory

Access Control

Ext Memory

Address

8051


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Pin Description of 8051 Mc

Vcc（pin 40)

Vcc provides supply voltage to the chip. The voltage source is +5V.

GND（pin 20)-ground

XTAL1 and XTAL2（pins 19,18)

These 2 pins provide external clock. Way 1：using a quartz crystal oscillator Way 2：using a TTL oscillator


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Pin Description of 8051 Mc RST(pin 9)：reset

It is an input pin and is active high（normally low）. The high pulse must be high at least 2 machine cycles. Upon applying a high pulse to RST, the microcontroller

will reset and all values in registers will be lost

/EA（pin 31):external access There is no on-chip ROM in 8031 and 8032 . The /EA pin is connected to GND to indicate the code is

stored externally. /PSEN ＆ ALE are used for external ROM. For 8051, /EA pin is connected to Vcc. The signal 0 is for external memory access and signal 1

for internal memory access B.Suresh, Asst.prof ,ECE

Department,ASIST,Paritala 6

Pin Description of 8051 Mc /PSEN（pin 29）：program store enable

This is an output pin and is connected to the OE pin of the ROM

This is acts as low to read external program code memory

ALE/PROG（pin 30）：address latch enable

It is an output pin and is active high.

8051 port 0 provides both address and data.

The ALE pin is used for de-multiplexing the address and data by connecting to the G pin of the 74LS373 latch.

This pin acts as program pulse input during on-chip EPROM programming


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I/O port pins

The four ports P0, P1, P2, and P3.

Each port uses 8 pins.

All I/O pins are bi-directional.

The ports has additional functionality also there except PORT 1


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PORT P1 (Pins 1 to 8):

The port P1 is a port dedicated for general I/O purpose. The other ports P0, P2 and P3 have dual roles in addition to their basic I/O function

PORT P0 (pins 32 to 39):

When the external memory access is required then Port P0 is multiplexed for address bus and data bus that can be used to access external memory in conjunction with port P2. P0 acts as A0-A7 in address bus and D0-D7 for port data. It can be used for general purpose I/O if no external memory presents.

PORT P2 (pins 21 to 28):

Similar to P0, the port P2 can also play a role (A8-A15) in the address bus in conjunction with PORT P0 to access external memory. B.Suresh, Asst.prof ,ECE



PORT P3 (Pins 10 to 17): In addition to acting as a normal I/O port P3.0 can be used for serial receive input pin(RXD) P3.1 can be used for serial transmit output pin(TXD) in a

serial port, P3.2 and P3.3 can be used as external interrupt pins(INT0’

and INT1’), P3.4 and P3.5 are used for external counter input pins(T0

and T1), P3.6 and P3.7 can be used as external data memory write

and read control signal pins(WR’ and RD’)read and write pins for memory access


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Architecture of 8051Mc

Accumulator(ACC):

The A Register acts as an operand register. the ACC has allotted an address in the on-chip special function register bank.

B-Register:

It is specially used for multiply and divide operations to store the one of the operand

Program status word(PSW):

this register contain the information about the status of the program. it reflects the status of the CPU. it is treated as special function register


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Stack Pointer(SP):

It is 8-bit wide. it will reside any where in the on-chip ROM. The stack pointer initialized to 07H after reset.

Data Pointer(DPTR):

It is used to hold 16-bit address. it is used as two independent registers as DPH(8-bit),DPL(8-bit)

Port 0 to 3 Latches and Drivers:

These are for four on-chip I/O ports .They acts like pairs



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Serial Data Buffer:

The serial data buffer internally contain two independent registers a transmit Buffer(PISO) register and Receive Buffer(SIPO)register.

The Serial Data Buffer identified by the SBUF and is one of the SFRs

Control Registers:

the SFRs ,IP,IE,TMOD,TCON,SCON and PCON contain the control and status information for interrupts ,timers/counter s and serial ports



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Timing and control unit:

This unit derives all necessary timing and control signal required for the internal operation of the circuit and also derives the control signal for the external system bus also

Oscillator:

The circuit generates the basic timing clock signal for the operation. Using crystal oscillator it generates the 12MHz clock

Instruction Register:

it decodes the opcode of an instruction to be executed and gives the information to the timing and control unit to generate the necessary signal for execution of the instruction



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EPROM and Program Address Register:

This block provides the on-chip EPROM and mechanism to internally address it.

RAM and RAM Address Register:

these block provides the internal 128 bytes of RAM and mechanism to address it internally.

ALU:

Arithmetic and Logic Unit

It uses the temporary Registers TMP1 and TMP2 to store the operands

It can not be accessed by the users



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SFR Register Bank:

This is a set of SFRs

Address range from 80H to FFH.

Interrupt , serial and timer units:

They control and perform their specified functions under the control timing and control unit



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Addressing Modes of 8051Mc

Direct addressing mode:

Operands specified by using the 8-bit address field in the instruction format

Only internal data RAM and SFRRs can be directly addressed

Ex: MOV Ro,90H(address of SFR P1)

Indirect Addressing Mode:

In this 8-bit operand address stored in register and is specified in the instruction

For this we can use Ro and R1 and Stack Pointer

Ex: add A@R1

B.Suresh, Asst.prof ,ECE


Register Addressing Mode:

in this mode operands are stored in the registers R0-R7 of the selected register bank . the register bank is selected using the two bits of PSW.

Ex: ADD A,R5

Register Specific Addressing mode:

In this mode the operand is implicitly specified using one of the registers.

Ex: RRA



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Immediate Addressing mode:

In this mode a constant is specified in the instruction

Ex: mov A,#120H

Indexed addressing mode:

Only program memory can be accessed using this addressing mode.

Ex: movc A,@A+DPTR(read program memory at A+DPTR)

movc A,@A+PC(read program memory at A+DPTR)



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A

B

R0

R1

R3

R4

R2

R5

R7

R6

DPH DPL

PC

DPTR

PC

Some 8051 16-bit Register

Some 8-bitt Registers of

the 8051

Register structure of 8051


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Register Structure of 8051Mc

Accumulator(ACC):

It is an operand register.

it is 8-bit wide

Address range 0EOH

B-Register:

It is specially used for multiply and divide operations to store the one of the operand.

The address range 0FOH

B.Suresh, Asst.prof ,ECE


Temporary Registers(TMP1 and TMP2):

They hold the operands temporarily.

They are not user accessible

These 8-bit wide each

Stack Pointer:

It is 8-bit wide. it will reside any where in the on-chip ROM. The stack pointer initialized to 07H after reset. this causes the stack to begin at location 08H

It uses the instructions PUSH and CALL



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Program Status word(PSW):

It is 8-bit Register It is given address range 0H0C in the SFRs address range It ha CY,AC,F0,RS1 and RS0,OV,P,X 1. CY – Carry flag 2. AC-Auxiliary carry flag 3. F0-general purpose status flag from user 4. RS1 and RS0-Register bank select bits 5. OV- Overflow flag 6. P-Parity flag 7. X-one user definable flag



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Data Pointer(DPTR):

It is used to hold 16-bit address. it is used as two independent registers as DPH(8-bit),DPL(8-bit)

These have address range 82H(DPH) and 83H(DPL) in the SFRs address range

Program counter(PC)and Program incremented:

These are 16-bit each

The PC holds the address of the next instruction to be executed

PC incremented increments the PC contents by one



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Serial Data Buffer:

It is a a16-bit Register

The address range 99H in the SFRs

The serial data buffer internally contain two independent registers a transmit Buffer(PISO) register and Receive Buffer(SIPO)register.

The Serial Data Buffer identified by the SBUF and is one of the SFRs



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EPROM and Program Address Register:

This is not available in all 8051 versions

This block provides the on-chip EPROM and mechanism to internally address it.

Program Address Register can address up to 4kB of memory

RAM and RAM Address Register:

these block provides the internal 128 bytes of RAM and mechanism to address it internally.



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Instruction Register:

it decodes the opcode of an instruction to be executed and gives the information to the timing and control unit to generate the necessary signal for execution of the instruction

Control Registers:

the SFRs IP,IR,TMOD,TCON,SCON, and PCON contain the control and status information

SFRs Register Bank:

This si a set of SFRs .which can be addressed using their respective address which lie in the range of 80H to FFH



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Thank you


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B.Suresh Asst professor ECE Department Pointer(SP): It is 8-bit wide. it will reside any where in...

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