11-12-2012, 02:40 PM
I/O Buses and Interfaces
IO Buses and Interfaces.ppt (Size: 708 KB / Downloads: 23)
There are many “standards” for I/O buses and interfaces
Standards allow “open architectures”
Many vendors can provide peripheral (I/O) devices for many different systems
Most systems support several I/O buses and I/O interfaces
Disk Interfaces
Examples
ATA – AT Attachment (named after IBM PC-AT)
IDE – Integrated Drive Electronics (same as ATA)
Enhanced IDE
Encompasses several older standards (ST-506/ST-412, IDE, ESDI, ATA-2, ATA-3, ATA-4)
Floppy disk
SCSI – Small Computer Systems Interface
ESDI – Enhanced Small Device Interface (mid-80s, obsolete)
PCMCIA
Communications Buses
For connecting systems to systems
Parallel/LPT
special purpose, e.g., using special software (Laplink) to transfer data between systems
Serial/RS232C
To connect a system to a voice-grade modem
Ethernet
To connect a system to a high-speed network
PCI (2 of 2)
Used for…
Just about any peripheral
Can support multiple high-performance devices
Graphics, full-motion video, SCSI, local area networks, etc.
Specifications
64-bit bus capability
Usually implemented as a 32-bit bus
Runs at 33 MHz or 66 MHz
At 33 MHz and a 32-bit bus, data rate is 133 Mbytes/s
RS-232C
History
Well-established standard, developed by the EIA (Electronics Industry Association) in 1960s
Originally intended as an electrical specification to connect computer terminals to modems
Defines the interface between a DTE and a DCE
DTE = Data Terminal Equipment (terminal)
DCE = Data Communications Equipment (modem)
A “modem” is sometimes called a “data set”
A “terminal” is anything at the “terminus” of the connection
VDT (video display terminal), computer, printer, etc.
Asynchronous Data Transmission
Data are transmitted on the TD (transmit data) line in packets, typically, of 7 or 8 bits
Each packet is “framed” by a “start bit” (0) at the beginning, and a “stop bit” (1) at the end
Optionally, a “parity bit” is inserted at the end of the packet (before the stop bit)
The parity bit establishes either “even parity” or “odd parity” with the data bits in the packet
E.g., even parity: the total number of bits “equal to 1” (including the data bits and the parity bit) is an “even number