Computer Architecture (Input Output Interface)

1. DON’T JUST SIT
THERE. YOU CAN
LEARN INPUT OUTPUT
INTERFACE IN QUICK
15 MINUTES.

2. Contents
Input Output Interface
I/O Bus and Interface Modules
I/O versus Memory Bus
Isolated (Port-Mapped) versus Memory-Mapped I/O
Example of I/O Interface

3. Input Output Interface
Internal storage & External I/O Devices
Direct Communication is not possible.
The major differences are:
 Different manner of operation
 Data transfer rate
 Difference in word format
 Difference in operating modes of peripherals

4. I/O Bus & Interface Module
Interface Interface Interface Interface
Keyboard
&
Display
Terminal
Printer
Magnetic
Disk
Magnetic
Tape
Data
Address
Control
I/O Bus
Processor
Fig. Connection of I/O Bus to input-output devices

5. IO Commands
There are four types of I/O Command:
 Control Command
 Status Command
 Output Data Command
 Input Data Command

6. I/O Versus Memory Bus
Like I/O Bus, Memory Bus also contains Data, Address
& Control Lines.
Three ways to communicate:
 Use two separate buses
 Use one common bus but separate control lines
 Use common bus with common control lines

7. Isolated versus Memory-Mapped I/O
ISOLATED I/O MEMORY MAPPED I/O
Separate read/write control
lines
A single set of read/write
control lines
Separate memory and I/O
address spaces
Common address space
Distinct input & output
instructions
No Specific input or output
instructions
- Considerable flexibility in
handling I/O operations

8. Example of an I/O Interface
I/O Data
Bus Buffers
Status
Register
Control
Register
Port B
Register
Port A
Register
CS
RS1
RS0
RD
WR
Timing
&
Control
Signal
InternalBus
Bidirectional
Data Bus
Chip Select
Register Select
I/O Read
I/O Write
To CPU To I/O Device
Control
I/O Data
Status
Fig. Example of an I/O Interface Unit