In real mode addressing for x86 cpus, memory is addressed with pairs of a segment and offset. The offset is added to the segment address multiplied by 16 to yield a 20-bit (20 binary digits, in other words, from the number 0 to (2^20)-1=1,048,575) address that points to a specific byte (8-bit number) in memory. Real mode is different than protected mode (which is used by Windows 95+, Linux on x86, etc) in that there is no segment protection, no inherent multitasking support, and it is possible to directly access the BIOS interrupts. Note also that the 20-bit address number prevents more than one (1) megabyte of memory from being addressed at a time.
Data can be accessed from memory by using the addressing modes, 8085 has 5 addressing modes namely,1. Immediate addressing mode 2. register addressing mode 3. direct addressing mode 4. indirect addressing mode 5. implied addressing mode
punched card
there are five addressing modes in 8086 they are : 1->direct addressing 2->Indirect addressing 3->index addressing 4->immediate addressing 5->register addressing
16-bit real mode is a CPU operating mode used primarily in x86 architecture, allowing the processor to access memory and execute instructions in a 16-bit environment. In this mode, the CPU operates with a memory address space limited to 1 MB and uses 16-bit segment and offset addressing. Real mode is the default mode upon system startup, enabling compatibility with older software and operating systems like MS-DOS. However, it lacks advanced features such as memory protection and multitasking found in protected mode.
To add the contents of a memory location to the contents of accumulator A, the direct addressing mode can be used. In this mode, the instruction specifies the actual memory address where the operand is located. The processor retrieves the value from that memory address and adds it directly to the contents of accumulator A. This method allows for straightforward access to the operand stored in memory.
protected mode
addressing modes helps the programmer to store or retrieve the data which is stored in any part of the data memory by addressing mode specified in the program.
Addressing modes of 8051 are 1.Immediate Addressing Mode 2.Register Addressing Mode 3.Register Indirect Addressing Mode 4.Direct Addressing Mode 5.Implied Addressing Mode and 6.Relative Addressing Mode
Ans: In the register addressing mode the operands are in registers which reside within the CPU. Register-mode instructions are 1-byte instructions and can be executed within the CPU without the need to reference memory for operands. But in the Register-indirect addressing mode the instruction specifies a register or a pair of registers in the processor whose contains give the address of the operand in memory. This mode uses 1-byte instructions even though the operand is in memory. Before using a register-indirect mode instruction, the programmer must ensure that the address of the operand is placed in the processor register with a previous transfer-type instruction. A reference to the register is then equivalent to specifying a memory address.
32 bit
32-bit flat memory mode.
In the 8086 microprocessor, register indirect addressing mode is a method of accessing data in memory using a register to hold the address of the data. In this mode, the effective address of the operand is provided by a register, such as BX, SI, or DI. This allows for flexible data manipulation, as the contents of the register can be easily modified to point to different memory locations. This addressing mode is particularly useful for operations on arrays and data structures.