8085 & 8086 Architecture — Practice MCQs for CCAT

Correct Answer: B — 8 bits

8085 is an 8-bit microprocessor with an 8-bit data bus for transferring data.

Correct Answer: B — 16 bits

8085 has a 16-bit address bus, allowing it to address up to 64KB (2^16) of memory.

Correct Answer: B — 6

8085 has 6 general-purpose 8-bit registers: B, C, D, E, H, and L, which can be paired as BC, DE, HL.

Correct Answer: A — Address Latch Enable - separates address from multiplexed bus

ALE (Address Latch Enable) signals when valid address is on the lower 8 bits of the multiplexed address/data bus.

Correct Answer: B — 5

8085 has 5 flags: Sign (S), Zero (Z), Auxiliary Carry (AC), Parity (P), and Carry (CY).

Correct Answer: B — 16 bits

8086 is a 16-bit microprocessor with a 16-bit data bus for transferring data.

Correct Answer: B — 20 bits

8086 has a 20-bit address bus, allowing it to address up to 1MB (2^20) of memory.

Correct Answer: B — BIU and EU

8086 has Bus Interface Unit (BIU) for fetching instructions and Execution Unit (EU) for executing them.

Correct Answer: B — Fetches instructions and handles bus operations

Bus Interface Unit (BIU) fetches instructions from memory, reads operands, and writes results to memory/ports.

Correct Answer: B — Decodes and executes instructions

Execution Unit (EU) decodes and executes instructions received from BIU using ALU and registers.

Correct Answer: B — 4

8086 has 4 segment registers: CS (Code), DS (Data), SS (Stack), and ES (Extra).

Correct Answer: B — Segment × 16 + Offset

Physical Address = Segment × 16 (shift left 4 bits) + Offset. This gives 20-bit address.

Correct Answer: C — 6 bytes

8086 has a 6-byte instruction prefetch queue in BIU for pipelining instruction fetch and execute.

Correct Answer: D — TRAP

TRAP is the highest priority interrupt in 8085 and is non-maskable.

Correct Answer: A — 003CH

RST 7.5 has vector address 003CH (7.5 × 8 = 60 = 3CH in hex).

Correct Answer: C — 5

8085 has 5 hardware interrupts: TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR.

Correct Answer: B — Single processor vs multiprocessor configuration

Minimum mode is for single processor, maximum mode is for multiprocessor systems with additional control signals.

Correct Answer: B — Primary register for arithmetic/logic operations

The accumulator (A register) is the primary register for ALU operations in 8085, storing one operand and the result.

Correct Answer: C — 64 KB

With 16-bit address bus, 8085 can address 2^16 = 65,536 bytes = 64 KB of memory.

Correct Answer: D — 1 MB

With 20-bit address bus, 8086 can address 2^20 = 1,048,576 bytes = 1 MB of memory.

Correct Answer: B — BX, SI, DI, BP

BX (Base), SI (Source Index), DI (Destination Index), and BP (Base Pointer) can be used for memory addressing.

Correct Answer: B — Set Interrupt Mask

SIM (Set Interrupt Mask) is used to mask/unmask RST interrupts and control serial output in 8085.

Correct Answer: B — Read Interrupt Mask

RIM (Read Interrupt Mask) reads the status of interrupt masks and serial input in 8085.

Correct Answer: B — BIU fetches while EU executes

8086 uses pipelining where BIU fetches next instruction while EU executes current instruction simultaneously.

Correct Answer: B — 8085 is 8-bit while 8086 is 16-bit with segmented memory

8085 is an 8-bit processor with 64KB memory, while 8086 is 16-bit with 1MB memory using segmented addressing.