The correct answer is: 2) RST 7.5

Explanation:

In the 8085 microprocessor, the RST 7.5 interrupt has unique characteristics:

• Edge-Triggered:
• RST 7.5 is positive-edge sensitive, meaning it triggers when the signal transitions from LOW to HIGH.
• It can be activated by a short pulse (minimum 500 ns wide).
   

Other RST Interrupts:

RST 6.5 and RST 5.5: Level-sensitive (require the signal to remain HIGH until acknowledged).

RST 4.5: Not a standard interrupt in 8085.6

The 8051 microcontroller has:

• 4 register banks

• Each bank contains 8 general-purpose registers: R0 to R7

• So, a total of 32 registers (4 banks × 8 registers)

 Details:

• The register banks are located in the lower 32 bytes (00H to 1FH) of the internal RAM.

• The current active bank is selected using RS0 and RS1 bits in the Program Status Word (PSW) register.

Let's trace the execution of the 8085 program step by step to determine the final content of the Accumulator (Register A).

Initial State:

• Register B contains an unknown value.
• Register A contains an unknown value.

Instruction 1: MVI B, 06h

• MVI stands for "Move Immediate".
• This instruction loads the immediate 8-bit value 06h into Register B.
• After this instruction:
  • Register B = 06_h

Instruction 2: MVI A, F2H

• This instruction loads the immediate 8-bit value F2h into the Accumulator (Register A).
• After this instruction:
  • Register A = F2_h

Instruction 3: ADD B

• ADD adds the content of the specified register (in this case, Register B) to the content of the Accumulator (Register A). The result is stored in the Accumulator.
• Before the addition:
  • Register A = F2_h
  • Register B = 06_h

Now, let's perform the hexadecimal addition:

   F2  (Hexadecimal)
+  06  (Hexadecimal)
-----

Starting from the rightmost digit:

• 2 + 6 = 8

Moving to the leftmost digit:

• F + 0 = F

Therefore, the result of the addition F2_h + 06_h is F8_h.

After the execution of the ADD B instruction, the content of the Accumulator (Register A) will be F8_h.

The correct answer is: 3) 20-2Fh

Explanation:
In the 8051 microcontroller, the bit-addressable memory area is a 16-byte range from 20H to 2FH in the internal RAM (data memory). This area contains 128 addressable bits (16 bytes × 8 bits per byte = 128 bits). Each bit in this region can be directly accessed using bit addresses from 00H to 7FH.

The other options:

1. 00-FFh - This is the entire internal RAM range, but only 20H-2FH is bit-addressable

2. 00-7Fh - This is the lower half of internal RAM (including SFRs), but not all is bit-addressable

3. 20-7Fh - This includes non-bit-addressable RAM beyond 2FH

8051 Microcontroller Special Function Registers

In the 8051 microcontroller, Special Function Registers (SFRs) are crucial for controlling specific functions and operations. These registers are essential for configuring and managing various aspects of the microcontroller's operation. The correct addressing range for these SFRs is from 80h to FFh. Let's delve into a detailed explanation of why this is the correct range and analyze other options as well.

Detailed Explanation of the Correct Option (Option 2: 80h - FFh)

In the 8051 microcontroller, Special Function Registers (SFRs) are located in the upper 128 bytes of the internal RAM address space. This means that SFRs are accessible using addresses from 80h to FFh. These registers are used to control various aspects of the microcontroller, such as timers, serial communication, port I/O, and interrupt control.

The SFRs are crucial for the following reasons:

• Control and Configuration: SFRs allow the user to configure and control the various hardware components of the 8051 microcontroller. For instance, the Timer Control Register (TCON) is used to control the operation of timers.
• Direct Access: SFRs provide direct access to specific hardware features, enabling efficient and precise control over the microcontroller's operations.
• Special Functions: As the name suggests, SFRs are used for special functions that are not typically handled by general-purpose registers. These include functions like interrupt priority, power control, and serial communication settings.

The SFRs are mapped to addresses from 80h to FFh, which is the upper half of the 256-byte internal RAM space. The lower half (00h to 7Fh) is used for general-purpose RAM and bit-addressable RAM. This separation ensures that the special functions have a dedicated address space, preventing conflicts with general-purpose RAM usage.

• 8051 is an 8-bit microcontroller built with 40 pins DIP (dual inline package).
• 8051 has internal RAM (128 Bytes) and ROM (4K Bytes).
• Of the 128-byte internal RAM, only 16 bytes are bit-addressable. The rest must be accessed in byte format.

Notes:

The Block Diagram of an 8051 microcontroller is as shown:

In an 8051 microcontroller,

• Internal RAM (data memory) - 128 bytes
• Internal memory (code memory) - 4 kB (ROM)
• Timer/counter - 2
• No. of interrupt - 5
• I/O pins - 32
• Serial port - 1

Registers in 8085 are primarily used to store temporary data.

General Purpose Registers:

• There are six 8-bit registers B, C, D, E, H, L. Each register contains 8 flip-flops hence, each register can store a maximum of 8 bit (1 Byte) of data.
• For storing data greater than 8 bits, these registers are used in pairs. There are three register pairs: BC pair, D – E pair, HL pair
• Each register pair can store a maximum of 16 bits of data (2 Byte).

Accumulator:

• It is an 8-bit register that contains 8 flip-flops. It can store a maximum of 8 bits of data.
• The importance of the accumulator is that, in most of the 8-bit arithmetic and logical operations, the microprocessor will always take the first 8-bit number from the accumulator.

Temporary Registers:

• There are three 8-bit registers W, X, and Z.
• Each register can store a maximum of 8 bits of data.
• These registers cannot be used or accessed by the programmer.
• These registers can be used only by the microprocessor for executing its operation i.e., the microprocessor will use these registers for the temporary storage of data.
• For storing 16-bit data W – Z pair can be used by the microprocessor.

• XRI F0H is used to complement the upper four bits of the accumulator in 8085.
• XRI 0FH is used to complement the lower four bits of the accumulator in 8085.
• ANI F0H is used to clear the lower four bits of the accumulator in 8085.
• ANI 0FH is used to clear the upper four bits of the accumulator in 8085.

Registers in 8085:

Registers are a type of computer memory used to quickly accept, store, and transfer data and instructions that are being used immediately by the processor.

Types of registers:

1.) General purpose registers:

• The 8085 has six general-purpose registers to store 8-bit data; these are identified as- B, C, D, E, H, and L. 
• These can be combined as register pairs – BC, DE, and HL, to perform some 16-bit operation.
• These registers are used to store or copy temporary data, by using instructions, during the execution of the program.

2.) Specific purpose registers:

a.) Accumulator: 

• The accumulator is an 8-bit register (can store 8-bit data) that is the part of the arithmetic and logical unit (ALU).
• After performing arithmetical or logical operations, the result is stored in accumulator.
• Accumulator is also defined as register A.

b.) Flag registers:

• These registers change their values as per the result of arithmetic operation.
• The 5 flag registers are: Sign flag, Carry flag, Auxiliary flag, Parity flag, Zero flag.

3.) Temporary registers:

• W and Z are two 8-bit temporary registers of 8085 microprocessor, which is not accessible to the user. 
• They are exclusively used for the internal operation by the microprocessor.

4.) Memory registers:

• There are two 16-bit registers used to hold memory addresses: Stack pointer and Program counter

Ports in 8051:

• There are 4 ports in 8051 IC (Port 0, Port 1, Port 2 and Port 3); 32 pins function as I/O port lines and 24 of these lines are dual-purpose (P0, P1, P3).
• Each can operate as I/O, or as a control line or part of the address or data bus.
• Eight lines in each port can be used in interfacing to parallel devices like printers, DAC, etc., or each line the port can be used in interfacing to single bit devices like LED’s, switches, transistors, solenoid, motors, and loudspeakers.

Important:

In an 8051 microcontroller,

• Internal RAM (data memory) - 128 bytes
• Internal memory (code memory) - 4 kB (ROM)
• Timer/counter - 2
• No. of interrupt - 5
• I/O pins - 32
• Serial port - 1

There is an 8-bit flag register out of which only 5 bits are used

Stack Pointer:

• The stack pointer in the 8085 microprocessor is a 16-bit register that stores the address of the top of stack memory.
• The value of the stack pointer is decremented by 2 in the PUSH operation.
• It will increment by 2 in POP operation.

Instruction cycle in 8085 microprocessor

The time required to execute and fetch an entire instruction is called the instruction cycle.

The seven Machine Cycle in 8085 Microprocessor are :

1.) Opcode Fetch Cycle: 

In this Machine Cycle in 8085, the processor places the contents of the Program Counter on the address lines, and through the reading process, reads the opcode of the instruction.

2.) Memory Read Cycle:​ 

The 8085 executes the memory read cycle to read the contents of R/W memory or ROM.

In this Machine Cycle in 8085, the processor places the address on the address lines from the stack pointer, general-purpose register pair, or program counter, and through the reading process, reads the data from the addressed memory location.

3.) Memory Write Cycle:

The 8085 executes the memory write cycle to store the data in data memory or stack memory.

The processor places the address on the address lines from the stack pointer or general-purpose register pair and through the writing process, stores the data in the addressed memory location.

4.) I/O Read:

The I/O Read cycle is executed by the processor to read a data byte from the I/O port or from the peripheral, which is I/O, mapped in the system.

5.) I/O Write:

The microprocessor uses the I/O Write machine cycle for sending a data byte to the I/O port or to the peripheral in I/O mapped I/O systems.

6.) Interrupt Acknowledge Cycle:

In response to the INTR signal, 8085 executes an interrupt acknowledge machine cycle to read an instruction from the external device. 

7.) Bus Idle Cycle:

Bus cycle of 8085 is used to access memory, peripheral devices (Input/Output devices), and Interrupt controller.

Concept:

• MOV A,#33H: This command will store the hexadecimal data 33H in the accumulator.
• ORL A,#01H: This command will OR the hexadecimal data 01H with accumulator data and store the resultant data in the accumulator.
• ANL A,#10H: This command will AND the hexadecimal data 10H with accumulator data.

​Calculation:

• During OR operation, if any of the two inputs will be high, then the output will be high.
• During AND operation, if any of the two inputs will be low, then the output will be low.

​

There are five types of interrupt in the 8051 microcontroller

1. Timer 0 overflow interrupt- TF0
2. Timer 1 overflow interrupt- TF1
3. External hardware interrupt- INT0
4. External hardware interrupt- INT1
5. Serial communication interrupt- RI/TI
    

The Timer and Serial interrupts are internally generated by the microcontroller, whereas the external interrupts are generated by additional interfacing devices or switches that are externally connected to the microcontroller.