The document discusses input/output organization in computers. It explains that all input/output devices connect to the computer via a bus that allows exchange of address, data and control signals. Each device is assigned a unique address. When the processor requests a read or write, the requested data is placed on the data lines and the address is sent to the address lines. Commonly used I/O mechanisms include interrupts and direct memory access. Memory mapped I/O allows I/O devices and memory to share the same address space.

1. Input/output
organIzatIon

2. Introduction
• The basic features of a computer is its ability to exchange
data with other devices.
• Input to the computer from various components from or
outside system.
• Output may also the same.

6. Accessing I/O Devices

7. Accessing I/O Devices
• All input/output devices can be connected to a computer
using bus it enables all devices to exchange information.
• It consists of three sets of lines used to carry address, data
and control signals.
• Each i/p / o/p device is assigned a unique set of addresses.
• When the processor request either a read (or) write
operation. Then, the requested data placed on data line and
corresponding address transferred over the address line and
activate control line based on the request.

8. • When the i/o devices and the memory share the same
address space, the arrangement is called Memory Mapped
I/O.
• For example if DATAIN is the address of the input buffer
associated with the keyboard, the instruction
» Move DATAIN, R0
• Reads the data from DATAIN and stores them into R0.
• Move R0,DATAOUT,
Sends the contents of register R0 to location
DATAOUT, which may be the output data buffer.

10. • Both the data and status registers are connected to the data
bus and assigned unique addresses.
• The address decoder, the data and status registers and the
control circuitry coordinate to create a interface circuit.
• Input/ output devices operate at speeds that are vastly
different form that of the processor speed.
• Program controlled I/O helps the processor to synchronize
the speed with i/o device by which frequently check the
status flag.
•

11. Commonly used mechanism
• Interrupts
• Direct memory access.

12. address range (
hexadecimal)
size device
0000 – 7FFF 32 KiB RAM
8000 – 80FF 256 bytes
general purpose
I/O
9000 – 90FF 256 bytes sound controller
A000 – A7FF 2 KiB
video
controller/text-
mapped display
RAM
C000 – FFFF 16 KiB ROM
Thus we might end up with a memory map like so: