io devies
DESCRIPTION
Bus conceptTRANSCRIPT
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Input/output organization
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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.
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Accessing I/O Devices
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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.
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• 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.
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• 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.
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Commonly used mechanism• Interrupts
• Direct memory access.
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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:
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