Intel 8085 & SAP-1 Microprocessor Architecture Sandbox
Step inside the heart of an 8-bit microprocessor. Inject custom 8085 assembly instructions (MVI, MOV, ADD, SUB, ANA, INR, XCHG, HLT), adjust clock speeds, trace data across the internal bidirectional bus, and watch register updates and ALU status flags in real time.
Target Objectives
- Trace logic flow and algorithm behavior step by step.
- Measure performance and complexity trade-offs.
- Experiment with structures and systems in a safe sandbox.
Theory & Core Foundations
A Microprocessor is a programmable, clock-driven electronic integrated circuit that fetches binary instructions from memory, decodes them into control signals, and executes arithmetic, logical, and data transfer operations. The Intel 8085 is a landmark 8-bit microprocessor architecture featuring an 8-bit internal data bus and a 16-bit address bus capable of addressing up to 64 KB of memory.
The core hardware datapath comprises five major functional subsystems:
- ALU & Accumulator (A) Subsystem: Performs 8-bit arithmetic (ADD, SUB) and Boolean logic (AND, OR, XOR), working in conjunction with an 8-bit Temporary Register (TR) and updating a 5-bit Flag Register ($S$, $Z$, $AC$, $P$, $CY$).
- Register Array: Six 8-bit general-purpose registers ($B$, $C$, $D$, $E$, $H$, $L$) that can be paired as 16-bit registers ($BC$, $DE$, $HL$, where $HL$ serves as the default memory pointer $[M]$).
- Special-Purpose Registers: 16-bit Program Counter (PC) (holding next instruction address) and 16-bit Stack Pointer (SP) (tracking LIFO top-of-stack).
- Timing & Control Matrix: Generates hardware synchronization and enable signals ($\overline{RD}$, $\overline{WR}$, $ALE$, $IO/\overline{M}$, $S_0$, $S_1$, $CLK$) across micro-state clock cycles ($T_1$ to $T_6$).
- Interrupt & Serial I/O Controller: Hardware pins for prioritized interrupts ($TRAP$, $RST\ 7.5$, $RST\ 6.5$, $RST\ 5.5$, $INTR$) and serial lines ($SID$, $SOD$).
Mathematical Foundations
Opcode Fetch (M1) requires 4 clock T-states (T1-T4), whereas standard Memory Read/Write cycles (M2, M3) require 3 T-states each. Microprocessor throughput is determined by total instruction T-state counts.
How The Simulation Works
Type any valid 8085 instruction into the interactive Assembly Console (e.g. 'MVI A, 45H', 'ADD B', 'MOV M, A') and click Execute, or select from the library of pre-loaded algorithms (Addition & Flags, HL Memory Transfer, Logic Operations, Subtraction). Adjust the clock frequency slider (0.5 Hz to 10 Hz) and use Run / Single Step buttons to follow data transfer across the glowing 8-bit bus, watch register values change, and inspect status flag updates.
Knowledge Graph & Related Concepts
Related Experiments & Simulations
Frequently Asked Questions
Learning Objectives
- •Trace the Fetch-Decode-Execute instruction cycle through machine cycles (M1 Opcode Fetch, M2 Memory Read/Write).
- •Identify the operational roles of the Accumulator (A), Temporary Register (TR), and 5 status flags (Sign, Zero, Auxiliary Carry, Parity, Carry).
- •Explain how tri-state buffers (High-Z) prevent bus contention on shared internal bidirectional data trunks.
- •Write and execute custom 8085 assembly instructions (MVI, MOV, ADD, SUB, ANA, ORA, XRA, INR, DCR, XCHG) in real time.
Real World Applications
- ✓Embedded Microcontroller Systems: Automotive engine control units (ECUs), industrial PLCs, and home appliance motor controllers.
- ✓Aerospace & Defense: Radiation-hardened microprocessors operating satellite flight computers and missile guidance telemetry.
- ✓Operating System Kernels: Low-level interrupt handling, register context switching, and stack pointer memory virtualization.
- ✓Compiler Design: Translating high-level programming language syntax (C/Rust) into machine opcode instructions and register allocations.