Interfacing_with_8257

1. Interfacing with 8257 (DMA Controller) Aryan Pandey Scholar No.: 23U02037

2. Introduction • The Intel 8257 is a Direct Memory Access (DMA) controller that transfers data directly between I/O devices and memory without CPU involvement. This improves speed and efficiency in data transfer operations.

3. Need for DMA • • CPU is slow compared to high-speed I/O devices. • • DMA allows direct data transfer between I/O and memory. • • Frees CPU for other tasks. • • Ideal for real-time and high-volume data transfer.

4. Features of 8257 • • 4 independent DMA channels. • • Each channel handles up to 16 KB of data. • • Supports fixed and rotating priority. • • Compatible with Intel 8085. • • Can operate in memory-to-I/O or I/O-to-memory mode.

5. Block Diagram of 8257 • The 8257 consists of Data Bus Buffer, Read/Write Logic, Control Logic, DMA Channels, and Priority Resolver. Data Bus Buffer Read/Write Logic Control Logic Priority Resolver DMA Channels

6. Pin Configuration • Key Pins: • • D0–D7: Data bus lines • • A0–A3: Address lines • • HRQ & HLDA: DMA request and hold acknowledge • • MEMR, MEMW, IOR, IOW: Control signals • • READY & TC: Synchronization and terminal count signals

7. Working Principle • Step 1: Peripheral sends DMA request (DRQ). • Step 2: 8257 sends HOLD to CPU. • Step 3: CPU acknowledges with HLDA. • Step 4: 8257 handles data transfer. • Step 5: Control returns to CPU after transfer.

8. DMA Operation Flowchart DMA Request • A simple representation of DMA operation steps. Bus Grant Address Generation Data Transfer Terminal Count Bus Release

9. Interfacing 8257 with 8085 • • 8257 connects to 8085 via data and address bus. • • HRQ and HLDA manage bus control. • • Control signals coordinate read/write operations. • • Ensures smooth data transfer during DMA cycles. 8085 CPU 8257 DMA

10. Timing Diagram (Overview) • Shows how signals HRQ, HLDA, MEMR, MEMW, IOR, and IOW interact during a DMA transfer. • Ensures proper coordination between CPU and peripherals.

11. Applications of 8257 • • High-speed data acquisition systems. • • Disk and tape drive controllers. • • Real-time graphics and display systems. • • Embedded systems requiring fast data movement.

12. Conclusion • The 8257 DMA controller offloads data transfer tasks from the CPU, increasing system efficiency and speed. • It plays a vital role in microprocessor-based systems.

13. Thank You! • — Aryan Pandey • Scholar No.: 23U02037