INPUT OUTPUT ARCHITECTURE (PART I)

1. EXTERNAL DEVICES

Can be classifies into three categories:

a. Human Readable

• Suitable for communicating with the computer user
• Example are video display terminals (VDT) and printers

b. Machine Readable

• Suitable for communicating with equipment
• Example are magnetic disk and type system,sensor and actuators

c. Communication

• Suitable for communicating with remote devices
• Allow a computer to exchange data with a remote device

 INPUT DEVICES

1. Keyboard
2. Mouse
3. Scanner
4. CD-Rom
5. Game Controller

Keyboard / Monitor

1. Most common means of computer / user interaction
2. Keyboard provides input that is transmitted to the computer
3. Monitor displays data provided by the computer
4. The character is the basic unit of exchange
5. Each character is associated with a 7 or 8 bit code

OUTPUT DEVICES

1. Monitor
2. Printer
3. Disk Drive
4. Floppy Drive
5. CDRW-Rom
6. Speakers

Disk Drive

1. Contains electronics for exchanging data, control, and status signals with an I/O
2. Contains electronics for controlling the disk read/write mechanism
3. Fixed-head disk – transducer converts between magnetic patterns on the disk surface and bits in the buffer
4. Moving-head disk – must move the disk arm rapidly across the surface

3. INPUT OUTPUT MODULE

Purpose of Input Output Module

• Interface to the processor and memory via the system bus or control switch
• Interface to one or more peripheral devices

Input Output Function

1. Control & Timing
2. CPU Communication
3. Device Communication
4. Data Buffering
5. Error Detection

Control & Timing

1. Processor checks input output modules for external device status
2. Input output returns status
3. If device ready, processor gives input output module command to request data transfer
4. Input output module gets a unit of data from device
5. Data transferred from the input output module to the processor

Processor Communication

Involve the following:

Command decoding - input output modules accepts command from the processor sent as signals on the control bus

Data - data exchanged between the processor and input output module over the data bus

Status reporting - common status signals BUSY and READY are used because peripherals are slow

Address recognition - input output must recognize a unique address for each peripherals that it control

Input Output Module Communication

• Device communication - commands, status information, and data
• Data buffering - data comes from main memory in rapid burst and must be buffered and the sent to the device's rate 
• Error detection - responsible for reporting error to the processor

Input Output Module Structure

• Module connects to the computer through a set of signal lines – system bus

• Data transferred to and from the module are buffered with data registers

• Status provided through status registers – may also act as control registers

• Module logic interacts with processor via a set of control signal lines

• Processor uses control signal lines to issue commands to the I/O module

• Module must recognize and generate addresses for devices it controls

• Module contains logic for device interfaces to the devices it controls

• I/O module functions allow the processor to view devices is a simple-minded way

• I/O module may hide device details from the processor so the processor only functions in terms of simple read and write operations – timing, formats

• I/O module may leave much of the work of controlling a device visible to the processor – rewind a tape

to be continued...

nadhiah amira nordin

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