# I/O Devices – Assignment: – EssaysForYou

Assignment Content

Question 1

In virtually all systems that include DMA modules, DMA to main memory is given higher priority than CPU access to main memory. Why?
Question 2
When a device interrupt occurs, how does the processor determine which device issued the interrupt?
Question 3
A system is based on an 8-bit microprocessor and has two I/O devices.

The I/O con- trollers for this system use separate control and status registers.
Both devices handle data on a 1-byte-at-a-time basis.
The first device has two status lines and three control lines.
The second device has three status lines and four control lines.

How many 8-bit I/O control module registers do we need for status reading and control of each device?
***Explain your reasoning and show your mathematical calculations on how you derived your answer

Question 4
A system is based on an 8-bit microprocessor and has two I/O devices.

The I/O con- trollers for this system use separate control and status registers.
Both devices handle data on a 1-byte-at-a-time basis.
The first device has two status lines and three control lines.
The second device has three status lines and four control lines.

What is the total number of needed control module registers given that the first device is an output-only device?
***Explain your reasoning and show your mathematical calculations on how you derived your answer
Question 5
A system is based on an 8-bit microprocessor and has two I/O devices.

The I/O con- trollers for this system use separate control and status registers.
Both devices handle data on a 1-byte-at-a-time basis.
The first device has two status lines and three control lines.
The second device has three status lines and four control lines.

How many distinct addresses are needed to control the two devices?
***Explain your reasoning and show your mathematical calculations on how you derived your answer
Question 6
Consider a microprocessor that has a block I/O transfer instruction such as that found on the Z8000.

Following its first execution, such an instruction takes five clock cycles to re-execute.
However, if we employ a nonblocking I/O instruction, it takes a total of 20 clock cycles for fetching and execution.

Calculate the increase in speed with the block I/O instruction when transferring blocks of 128 bytes.
**Explain your reasoning and show your mathematical calculations on how you derived your answer
Question 7

What is the difference between memory-mapped I/O and isolated I/O?

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