Information

45.2.1 Detailed signal descriptions
The detailed signal descriptions of the UART are shown in the following table.
Table 45-2. UART—Detailed signal descriptions
Signal I/O Description
CTS I Clear to send. Indicates whether the UART can start transmitting data when flow control is
enabled.
State meaning Asserted—Data transmission can start.
Negated—Data transmission cannot start.
Timing Assertion—When transmitting device's RTS asserts.
Negation—When transmitting device's RTS deasserts.
RTS O Request to send. When driven by the receiver, indicates whether the UART is ready to
receive data. When driven by the transmitter, can enable an external transceiver during
transmission.
State
Meaning
Asserted—When driven by the receiver, ready to receive data. When
driven by the transmitter, enable the external transmitter.
Negated—When driven by the receiver, not ready to receive data. When
driven by the transmitter, disable the external transmitter.
Timing Assertion—Can occur at any time; can assert asynchronously to the other
input signals.
Negation—Can occur at any time; can deassert asynchronously to the
other input signals.
RXD I Receive data. Serial data input to receiver.
State meaning Whether RXD is interpreted as a 1 or 0 depends on the bit encoding
method along with other configuration settings.
Timing Sampled at a frequency determined by the module clock divided by the
baud rate.
TXD O Transmit data. Serial data output from transmitter.
State meaning Whether TXD is interpreted as a 1 or 0 depends on the bit encoding
method along with other configuration settings.
Timing Driven at the beginning or within a bit time according to the bit encoding
method along with other configuration settings. Otherwise, transmissions
are independent of reception timing.
Collision I Collision Detect. Indicates if a collision is detected during Data Transmission.
State
Meaning
Asserted—Indicates a collision detection. UARTxCPW determines the
length of this pulse for valid collision detection.
Negated—No collision detected.
Timing Asserts asynchronously to other input signals.
Chapter 45 Universal Asynchronous Receiver/Transmitter (UART)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 1043