Architecture and Features of 8081 Microcontroller

Architecture and Features of 8081 Microcontroller

1. It has an 8-bit data bus and an 8-bit ALU.

2. It has a 16-bit Address bus i.e., 64kb of RAM and ROM.

3. It has RAM (data memory) of 128-bit and ROM (Program Memory) of 4kb.

4. It consists of three internal and two external interrupts.

5. It consists of a 16-bit program counter and data pointer (DPTR).

6. It has 32 general purposes registered each 8-bit.

7. It also consists of two 16-bit timers/counters.

8. Less power use in 8051 concerning other microcontrollers.

Architecture Diagram Of 8051 Microcontroller:

ALU (Arithmetic Logical Unit):

ALU is used to perform all Arithmetic and logical operations such as addition, subtraction, multiplication, division, ANDing, ORingand, XORing, Rotate, Clear, and complement operations.

Program Counter:

1. The 16-bit program counter register is an engine that starts the progress execution and indicates the address in memory from which no instruction is to be reached.

2. Immediately after its execution the value of the program counter incremented by 1.

3. However, the program counter value put changes any movement that will cause a “JUMP” to a new location in the program memory.

4. This is how subroutine or branch instruction is executed.

B Register:

1. B Register is used during multiply and divide operation which can be performed only upon the number stored in A and B Register.

2. This Register is used to store one of the operants for multiply and divide instruction.

3. This Register is considered a special Function Register (SFR).

Data Pointer Register (DPR):

1. It is a 16-bit Register that consists of 16 flip-flops this 16-bit register can be split into an 8-bit Register in two 8-bit registers.

2. The higher byte register can be represented by DPTR.

3. Data pointer higher (DPH) is register and lower bit register can be represented by DPL.

4. This register is not a true one because it physically does not exist.

Instruction Register (IR):

This register decodes on provide of an instruction to be executed and gives information to the timing and control unit to generate a necessary signal for the executive of the instruction.

Stack Pointer:

1. This is the 8-bit Register.

2. The Content of this Register is decremented before the data is stored in the stack using push or call instructions.

3. This register contains an 8-bit top-of-stack address.

4. The stack may be defined anywhere in the on-chip 128-byte RAM.

5. After Resetting the stack pointer (SP) register is initialized to 07.

Serial Data Buffer:

1. The serial data buffer internally contains to independent Register.

2. One of them is a transmit buffer which is necessary for a parallel in the serial-out register.

3. The other is called receive buffer which is a serial-in 2 parallel-out register.

Accumulator ( A Register ):

1. The Accumulator is one of the most SFR (Special Function Register) on the 8051 since it is involved in so many instructions.

2. This is a general-purpose register that is used to store results after an operation.

3. Once an arithmetical Operation is performed by ALU, the result is loaded into the accumulator.

PSW Register (Program Status Ward):

This is a set of flags containing the status information of the operation performed by microcontroller 8051.

Carry Flag (CY):

1. If an operation performs in ALU Generation a carry from D7 bit to the next stage the carry flag is set to ‘1’.

2. If there is a no carry/borrow out of the most significant bit D7 of the result then the carry flag is reset to ‘0’.

Auxiliary Carry Flag (AC):

1. If an operation performed in the ALU generates a carry From D3 to D4 then the auxiliary carry flag is set to be ‘1’ otherwise Reset to ‘0’.

2. This is not a general-purpose flag it is used only by the microcontroller.

Parity Flag:

1. This bit is used to indicate the parity of the result.

2. If the result contains an even number of ‘1’ this flag is set to be ‘1’.

3. If the contents of the results odd number of ‘1’ then this flag is reset to ‘0’.

F0 (Flag 0):

1. This is a general-purpose bit.

2. It is available to the user.

Bit 1 :

This bit is used for the future version of a microcontroller.

OV (Over Flow Flag):

1. Overflow occurs when the result of an arithmetic operation is too large so that it can not be stored in one register.

2. In that case, this flag bit will be set to ‘1’.

3. If there is no overflow this flag bit will be reset to ‘0’

RS1 – RS0 (Register Bank Select Bits):

1. These 2 bits are used to select one of the 4 register banks in internal RAM shown in Table.

2. By writing zeros and one to this bit A group of register R0 – R1 can be used out of 4 Register banks in internal RAM.

Timer Register :

1. This is a 16-bit Register.

2. There are two timer registers one is timer ‘0’ and another one is timer ‘1’.

3. Each timer register can be split into two 8-bit registers.

4. For timer ‘0’ the higher 8-bit Register is represented by TH0 and the lower 8-bit Register TL0.

5. For timer ‘1’ the higher 8-bit Register is represented by TH1 and the lower is represented by TL1.

Timer 0 (16-bit).

Timer 1 (16-bit)

Control Register :

The special function Register IP, IE, IMOD, ICON, SCON, PCON content control, and status information for interrupt timer/counter and serial ports.

Timing and Control Units:

1. This Unit drives all the necessary timing and control signals required for the internal operation of the circuit.

2. It also drives the control signal required for controlling the external system bus.