Data transfer details of 8085

1. Data Transfer
Techniques
Md. Motaleb Hossen Manik
Lecturer
Dept. of CSE, KUET

2. Types
• Programmed
• Data transfer occurs between CPU and I/O
• Controlled by a code located in memory
• DMA
• Bypasses CPU
• Transfers data directly to or from memory and I/O

3. Modes
• Synchronous
• Asynchronous
• Interrupt driven

4. Interrupt Driven

5. DMA Mode of Data Transfer

6. DMA Mode of Data Transfer

7. MPU Features
• An input control line
• An output control line
• Tristate the address, data and necessary control line

8. DMA Controller Features
• Interfaces the MPU buses with the I/O device
• Generate DMA request signal
• In response to the DMA grant signal from the MPU, it
must control the address bus and control line needed for
data transfer
• It must hold the information bytes to be transferred

9. Modes of DMA
• Blocked DMA mode
• Continues data transmission once initialized
• Cycle stealing mode
• Takes control of the bus to transfer one byte and then returns
control to the CPU

10. I/O Port
• Connects I/O devices with the processor
• Speed of every I/O device is not the same
• I/O port maintains a buffer

11. I/O Port Components
• Device selection logic
• Data buffers
• Bus drivers
• Status flag register
• Control line

12. Types of I/O Ports
• Programmable (8255 A)
• Non-programmable (8212)

13. Components of Programmable
I/O Port
• Capability for directly interacting with the system bus
• Device selection logic
• Buffer register
• Control command register
• Indicates the mode of data transfer
• Status register
• Read/Write and control logic

14. Serial Mode of Data Transfer
• Transfers bitwise data
• Why needed?
• Minimizes cabling
• Less complexity
• Cost reduction
• Availability of suitable serial communication media
• Telephone network, microwave link
• Inherent characteristics of many I/O devices

15. Types of Serial Communication
• Simplex
• Half-duplex
• Full-duplex
Sender Receiver
Sender Receiver
Sender Receiver

16. Some Terms
• Baud Rate
• The rate of transmission of data in serial mode is specified by the
number of bits per second transferred
• It varies from 75 to 19200
• Split Bit Mode
• Transmitter and receiver have a different bit rate

17. References
• Microprocessors Principles and Applications by Ajit Pal