uart

uart

Universal Asynchronous
Receiver/Transmitter
UART

ECEn/CS 224

20 UART
Page 1

© 2003-2006
BYU

Why use a UART?
• A UART may be used when:
– High speed is not required
– A cheap communication line between two devices
is required
• Asynchronous serial communication is very cheap
– Requires a transmitter and/or receiver
– Single wire for each direction (plus ground wire)
– Relatively simple hardware
– Asynchronous because the
• PC devices such as mice and modems used to often
be asynchronous serial devices
ECEn/CS 224

20 UART
Page 2

© 2003-2006
BYU

UART Uses
• PC serial port is a UART!
• Serializes data to be sent over serial cable
– De-serializes received data
Serial
Port

Serial
Cable

Serial
Port

Serial
Cable

Device

ECEn/CS 224

20 UART
Page 3

© 2003-2006
BYU

UART Uses
• Communication between distant computers
– Serializes data to be sent to modem
– De-serializes data received from modem
Serial
Cable

Phone
Line
Phone
Line

Serial
Cable

Modem

Modem

ECEn/CS 224

20 UART
Page 4

© 2003-2006
BYU

UART Uses
• Used to be commonly used for internet access

Phone
Line

Internet
Internet

Phone
Line

Serial
Cable

Modem

ECEn/CS 224

20 UART
Page 5

© 2003-2006
BYU

UART Uses
• Used to be used for mainframe access
– A mainframe could have dozens of serial ports
Mainframe

Serial
Cables

Terminal

Terminal
Terminal

Terminal

ECEn/CS 224

20 UART
Page 6

© 2003-2006
BYU

UART Uses
• Becoming much less common
• Largely been replaced by faster, more
sophisticated interfaces
– PCs: USB (peripherals), Ethernet (networking)
– Chip to chip: I2C, SPI

• Still used today when simple low speed
communication is needed

ECEn/CS 224

20 UART
Page 7

© 2003-2006
BYU

UART Functions
• Outbound data
– Convert from parallel to serial
– Add start and stop delineators (bits)
– Add parity bit

• Inbound data
–...