1. A system is based on an 8-bit microprocessor and has two I/O devices. The I/O controllers 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.
a. How many 8-bit I/O control module registers do we need for status reading and control of
each device?
Answer:
b. What is the total number of needed control module registers given that the first device is
an output-only device?
Answer:
c. How many distinct addresses are needed to control the two devices?
Answer:
2. A DMA module is transferring characters to memory using cycle stealing from a device
transmitting at 9600 bps. The processor is fetching instructions at the rate of 1 million
instructions per second (1 MIPS). By how much will the processor be slowed down due to the
DMA activity?
Answer:
3. Consider a system in which bus cycles takes 500 ns. Transfer of bus control in either
direction, from processor to I/O device or vice versa, takes 250 ns. One of the I/O devices has a data transfer rate of 50 KB/s and employs DMA. Data are transferred 1 byte at a time.
a. Suppose we employ DMA in a burst mode. That is, the DMA interface gains bus
mastership prior to the start of a block transfer and maintains control of the bus until the
whole block is transferred. For how long would the device tie up the bus when
transferring a block of 128 bytes?
Answer:
