Module 5. Input and
Types of data transfer mode
• Programmed I/O
• Interrupt driven I/O
• DMA (Direct Memory Access)
1. Address the Device.
2. Check its status.
3. IF ready
check another device
Interrupt driven I/O
• Device interrupt’s CPU
• CPU acknowledge the
• CPU perform operation
Direct Memory Access
• CPU call DMA for
• It will allow the device to
access memory directly.
Need of DMA
• DMA, or Direct Memory Access, is a sub controller
that can access memory in sequential order without
intervention from the processor. DMA is used to
moving around large amounts of data in the
computer without taking time away from the
• The first major uses of DMA included drive
controllers and sound cards.
Basic operation’s of DMA
• DMA provide direct access to memory.
• For fast operation DMA work as a bus master.
• Direct Memory Access is a method of transferring
data between peripherals and memory without using
DMA Data Transfer
• It is data transfer technique directly between memory
and I/O without CPU intervention.
• Under the supervision of extra hardware called
DMA controller .
• Fastest type of data transfer technique among this
• 1. The I/O device asserts DRQ signal.
• 2. DMA controller send HOLD signal to
• 3. microprocessor Send HLDA to DMA Controller& DMA
Takes charge of system bus.
• 4. DMA give DMA ACK(back) signal to I/O devices
• 5.now, DMA controller places memory address on address bus
and data bytes from memory transfer to I/O .
• 6.DMA Controller updates memory address register and word
• 7. when internal count = 0 then DMA Controller sets
• 8. now processor regain the charge od the system bus which
continues the normal operation.
Types DMA based data transfer
• Byte /cycle stealing mode.
• Burst /demand mode.
• Continuous / block mode.