8086 Microprocessor Types (Type 1, 2, 3, 4)
The 8086 microprocessor is a 16-bit CPU. It has different types based on how it handles the instruction queue, control signals, and single/multi-processor configuration.
Type 1: Minimum Mode Single-Processor System
- Mode: Minimum mode (MN/MX = 0)
- Control signals: CPU generates all signals itself
- Use: Single 8086 CPU in a system
- Example signals: RD, WR, ALE, READY all from CPU
Type 2: Maximum Mode Multi-Processor System
- Mode: Maximum mode (MN/MX = 1)
- Control signals: CPU uses status signals (S2, S1, S0); external bus controller (8288) generates actual control signals
- Use: Multiprocessor or coprocessor system (e.g., 8086 + 8087)
Type 3: Minimum Mode with Wait States and Memory Interfacing
- Basically Type 1 + wait states
- Used when memory is slower than CPU
- CPU inserts wait states to prevent memory overrun
- Signals like READY, HOLD, HLDA are used
Type 4: Maximum Mode with Coprocessor / Multiprocessor Interfacing
- Basically Type 2 + wait states / memory interfacing
- Designed for multi-processor + slow memory
- Uses 8288 bus controller along with READY and HOLD signals
Summary Table
| Type | Mode | Use Case | Control Signals |
|---|---|---|---|
| 1 | Minimum | Single CPU system | CPU generates directly |
| 2 | Maximum | Multi CPU / coprocessor system | 8288 bus controller generates |
| 3 | Minimum + wait | Single CPU, slow memory | Wait states added |
| 4 | Maximum + wait | Multi CPU, slow memory | 8288 bus controller + wait states |
Summary
- Minimum mode → single CPU → Type 1 or 3
- Maximum mode → multi CPU → Type 2 or 4
- Slow memory → wait states → Type 3 or 4