Interfacing_with _8257_Aryan_Pandey.pptx

DMA CONTROLLER 8257

1. Interfacing with 8257 (DMA Controller) Aryan Pandey Scholar No.: 23U02037 IIIT Bhopal Subject: Microprocessor and Microcontroller

2. Introduction The Intel 8257 is a Direct Memory Access (DMA) controller used to transfer data directly between I/O devices and memory without CPU intervention. It improves system performance by freeing the CPU from data transfer tasks.

3. Need for DMA • Programmed I/O and Interrupt-driven I/O waste CPU time. • DMA allows peripherals to directly access memory. • Useful for high-speed data transfer applications such as disk drives, ADC/DAC, etc.

4. Features of 8257 • 4 independent DMA channels. • Each channel can transfer up to 16 KB of data. • Fixed and rotating priority modes. • Memory-to-I/O and I/O-to-memory transfers. • Compatible with 8085/8086 microprocessors.

5. Block Diagram of 8257 The 8257 consists of: • Data bus buffer • Read/Write logic • Control logic • Priority resolver • DMA channels and address registers It manages DMA requests and data transfers between memory and peripherals.

6. Pin Configuration Important pins: • D0–D7: Data bus lines • A0–A3: Address lines • HRQ/HLDA: DMA handshake signals • MEMR, MEMW, IOR, IOW: Control signals • TC: Terminal count output • READY: Synchronization signal

7. Working Principle Step 1: Peripheral sends DMA request (DRQ) to 8257. Step 2: 8257 sends HOLD to CPU. Step 3: CPU acknowledges via HLDA. Step 4: 8257 transfers data between I/O and memory. Step 5: After completion, control is returned to CPU.

8. DMA Operation Flowchart DMA Operation Steps: 1. DMA Request 2. CPU Grants Bus 3. Address Generation 4. Data Transfer 5. Terminal Count 6. Bus Released

9. Interfacing 8257 with 8085 • 8257 connected to 8085 via data and address bus. • HRQ and HLDA used for DMA control. • Control signals manage read/write operations. The 8085 temporarily halts execution while 8257 transfers data.

10. Timing Diagram (Overview) The timing diagram shows how signals like HRQ, HLDA, MEMR, MEMW, and IOR/IOW coordinate during DMA transfer. It ensures synchronized operation between CPU, 8257, and peripheral.

11. Applications of 8257 • Used in microprocessor-based systems for high-speed data transfer. • Disk and tape data transfer. • Real-time data acquisition. • Graphics and display systems.

12. Conclusion The 8257 DMA controller enhances data transfer efficiency by reducing CPU load. It is an essential component in systems requiring high-speed, low-latency communication between memory and peripherals.

13. References • Microprocessor Architecture, Programming, and Applications with the 8085 – Ramesh S. Gaonkar • Intel 8257 Datasheet • IIIT Bhopal Lecture Notes