docs(notes): add io interface notes

Author: lzwjava

Diff for: notes/2025-04-15-io-interface-en.md

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+---
+title:  I/O and Interface Technology
+lang: en
+layout: post
+audio: false
+translated: false
+generated: true
+---
+
+Great! Here's a **comprehensive tutorial** for **Part 4: I/O and Interface Technology**, based on your course outline. This tutorial is structured to explain concepts clearly, provide practical examples, and show how components like 8255A, 8253/8254, and 8251A work together in a microcomputer system.
+
+---
+
+## 📘 Part 4: I/O and Interface Technology
+
+---
+
+### **1. Basics of I/O Interfaces**
+
+#### ✅ Port Addressing
+
+I/O interfaces allow a microprocessor to communicate with external devices. There are **two main addressing schemes**:
+
+- **Memory-Mapped I/O**:
+  - I/O devices are treated like memory locations.
+  - Uses the same instructions as memory access (e.g., `MOV`).
+  - Pros: Larger address space, can use all CPU instructions.
+  - Cons: Consumes memory address space.
+
+- **Isolated I/O (Port-Mapped I/O)**:
+  - Special instructions like `IN` and `OUT`.
+  - Limited address space (usually 256 ports).
+  - Separate address space from memory.
+
+| Type             | Instruction Set Used | Address Space     |
+|------------------|----------------------|-------------------|
+| Memory-Mapped    | `MOV`, etc.          | Part of memory    |
+| Isolated (I/O-Mapped) | `IN`, `OUT`      | Separate I/O space|
+
+---
+
+#### ✅ Data Transfer Modes
+
+1. **Program-Controlled I/O**:
+   - CPU checks device status and reads/writes data directly.
+   - Simple but inefficient (busy waiting).
+
+2. **Interrupt-Driven I/O**:
+   - Device notifies CPU when it's ready via an **interrupt**.
+   - CPU executes an Interrupt Service Routine (ISR).
+   - Improves efficiency.
+
+3. **DMA (Direct Memory Access)**:
+   - Device transfers data directly to/from memory.
+   - Bypasses CPU for large/fast data transfer.
+   - Used for high-speed devices like disks.
+
+---
+
+### **2. Interrupt Systems**
+
+#### ✅ Interrupt Vector Table
+
+- Stores addresses of **Interrupt Service Routines (ISRs)**.
+- Each interrupt type has a **unique vector** (e.g., INT 0x08 for Timer).
+- The CPU looks up the table to jump to the correct ISR.
+
+#### ✅ Priority Handling
+
+- When multiple interrupts occur simultaneously, **priority** determines which gets handled first.
+- Priority can be **fixed** or **programmable**.
+
+#### ✅ 8259A Programmable Interrupt Controller
+
+- Manages multiple interrupt sources (up to 8).
+- Can be **cascaded** for 64 interrupt inputs.
+- Key functions:
+  - Interrupt masking.
+  - Priority setting.
+  - Sending interrupt vector to CPU.
+
+**Registers**:
+- IMR (Interrupt Mask Register)
+- ISR (In-Service Register)
+- IRR (Interrupt Request Register)
+
+**Example**: Keyboard and Timer both trigger interrupts — 8259A prioritizes them based on configured priority.
+
+---
+
+### **3. Common Interface Chips**
+
+---
+
+#### ✅ 8255A Programmable Peripheral Interface (PPI)
+
+Used to interface with external parallel devices like switches, LEDs, etc.
+
+- Has 3 ports: **Port A**, **Port B**, and **Port C**.
+- Controlled via **Control Word**.
+
+**Modes of Operation**:
+
+- **Mode 0** – Simple I/O
+  - Each port can be input/output.
+- **Mode 1** – Handshaking I/O
+  - Supports synchronization with peripheral.
+- **Mode 2** – Bidirectional I/O (only for Port A)
+  - Two-way data transfer with handshaking.
+
+**Example**:
+- Port A: output to LED display
+- Port B: input from DIP switches
+- Port C: used for control signals
+
+---
+
+#### ✅ 8253 / 8254 Programmable Interval Timer
+
+Used for generating delays, baud rates, etc.
+
+- Has 3 independent 16-bit counters.
+- Each counter has modes (0–5), e.g.:
+
+| Mode | Description               |
+|------|---------------------------|
+| 0    | Interrupt on terminal count |
+| 2    | Rate generator (e.g., for clock) |
+| 3    | Square wave generator     |
+
+**Applications**:
+- Delay generation
+- Real-time clock
+- Baud rate generation for serial ports
+
+**Typical Use**:
+- Counter 0: OS timer tick
+- Counter 1: DRAM refresh
+- Counter 2: Speaker tone
+
+---
+
+#### ✅ 8251A USART (Universal Synchronous/Asynchronous Receiver Transmitter)
+
+Used for **serial communication**.
+
+- Converts between parallel and serial data.
+- Supports both:
+  - **Synchronous**: requires clock signal
+  - **Asynchronous**: uses start/stop bits
+
+**Key Features**:
+- Baud rate control (via 8253/8254)
+- Configurable character length, stop bits, parity
+- Supports transmit and receive buffering
+
+**Application**: Serial port communication with PC or microcontroller.
+
+---
+
+## ✅ Summary Table
+
+| Chip   | Function                   | Key Features                          |
+|--------|----------------------------|----------------------------------------|
+| 8255A  | Parallel I/O               | 3 ports, 3 modes, handshaking          |
+| 8253/54| Timing/counting            | 3 counters, multiple modes             |
+| 8251A  | Serial communication       | Sync/Async, baud control               |
+| 8259A  | Interrupt control          | Priority, masking, ISR vectoring       |
+
+---
+
+## 🧠 Real-World Example Scenario
+
+You want to design a simple microcomputer system to:
+
+- Control an LED matrix via Port A (8255A Mode 0)
+- Receive keyboard input via interrupts (8259A)
+- Generate a periodic system tick every 1ms (8253 Mode 2)
+- Send sensor data to PC via serial (8251A in async mode)
+
+Each chip would be configured and connected to the CPU through address decoding and control signals, with appropriate software written to manage communication.
+
+---
+
+Let me know if you want example code, simulation diagrams, or a quiz for this chapter!