Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 1 Part 3: Understand I/O in Computer System, Asynchronous Serial…
Chapter 1 Part 3: Understand I/O in Computer System
Learning Outcomes
Define I/O Module
Draw the I/O Module diagram
List I/O devices
Describe the I/O bus and interface module
I/O Data transfer
Asynchronous serial transmission is character oriented.
Each character transmitter consists of a start bit,
character bits, and stop bits.
The first bit is called the start bit. It is always a 0 and is
used to indicate the beginning of a character.
The last bit called the stop bit is always a 1. In
asynchronous transmission, binary information is sent only when it is available and the line remains idle when
there is no information to be transmitted.
Transmission of data without the use of an
external clock signal, where data can be transmitted continuously rather than in a steady
stream.
The most significant aspect of asynchronous
communications is variable bit rate, or that the transmitter and receiver clock generators do not
have to be exactly synchronized.
Characteristic of isolated and memory mapped I/O
Memory mapped I/O
Devices and memory share an address
space
I/O looks just like memory read/write
No special commands for I/O
Large selection of memory access
commands available
Isolated I/O
Separate address spaces
Need I/O or memory select lines
Special commands for I/O
Limited set
Transfer mode
Programmed I/O
• Interrupt-Initiated I/O
• Direct Memory Access
Programmed I/O
Method of transferring data between
the CPU and a peripheral
Happens when software running on the CPU
The best known example of a PC device that
uses programmed I/O is the ATA interface.
Refers to using input and
output instructions to transfer data
Data are exchanged between the CPU and the I/O
module.
The CPU executes a program that gives it direct
control of the I/O operation
When CPU issues a command to I/O module, it
must wait until I/O operation is complete.
If the CPU is faster than I/O module, there is
wastage of CPU time.
Advantage
– Simple to implement
Disadvantage
– CPU is tied up for the duration of the transfer
while doing a relatively simple task
Interrupt-initiated I/O
Overcomes CPU waiting
No repeated CPU checking of device
I/O module interrupts when ready
DMA
Transferring data between peripherals and
memory without using the CPU.
Sometimes, CPU may not be fast enough to
keep up with the peripheral.
Special-purpose processor called a DMAC can be used to transfer data between memory and I/O devices.
DMAC
Periodically takes over
control of the system bus from the CPU.
Generates address, data and control
signals to transfer data between memory and
I/O devices
Asynchronous Serial Transfer
Asynchronous Communication Interface