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• Largely been replaced by faster, more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
–...