8085 Microprocessor Architecture

Why it matters

The 8085 microprocessor architecture is fundamental for students pursuing electronics and telecommunication engineering. Understanding this architecture is crucial for designing and analyzing microprocessor-based systems, which are integral to modern electronics and embedded systems.

Key ideas

• Architecture Overview: The 8085 microprocessor is an 8-bit microprocessor with a 16-bit address bus, allowing it to address 64 KiB of memory. It has a simple architecture that includes an Arithmetic and Logic Unit (ALU), registers, a control unit, and a clock generator.
• Registers: The 8085 has six general-purpose registers (B, C, D, E, H, L), each 8 bits wide, which can be paired to perform 16-bit operations. It also includes an Accumulator (A), a Flag register, a Stack Pointer (SP), and a Program Counter (PC).
• Instruction Set: The 8085 supports a variety of instructions, including data transfer, arithmetic, logical, control, and branching instructions.
• Control and Timing: The microprocessor uses control signals to manage data flow and timing signals to synchronize operations.
• Interrupts: The 8085 supports five hardware interrupts, which allow it to respond to external events.

Formulas

• Number of addressable locations = 2^n where n is the number of address lines (unitless).

Worked example

Problem: Calculate the maximum memory size that can be addressed by the 8085 microprocessor.

Given:

• Number of address lines, n = 16

Steps:

1. Use the formula for memory address range: Memory Address Range = 2^n
2. Substitute the given value: Memory Address Range = 2^16
3. Calculate: Memory Address Range = 65536
4. Convert to kilobytes: 65536 bytes = 64 KiB

Answer: The maximum memory size that can be addressed by the 8085 microprocessor is 64 KiB.

The byte-addressed memory range is 0000H through FFFFH. A 16-bit address bus specifies address space, not installed RAM. The low eight address bits share pins with the data bus and are latched using ALE; an address bus width is distinct from data width.

Common mistakes

• Confusing the data bus width with the address bus width.
• Forgetting to pair registers for 16-bit operations.
• Misunderstanding the role of the Program Counter and Stack Pointer.

For GATE EC

Questions on the 8085 microprocessor architecture often involve calculating memory size, understanding register operations, and analyzing instruction execution. Practice problems on memory addressing and instruction cycles are beneficial.

Quick check

1. What is the width of the data bus in the 8085 microprocessor?
2. How many general-purpose registers does the 8085 have?
3. What is the maximum memory size addressable by the 8085?

Answers: 1. 8 bits 2. Six 3. 64 KiB