NXP Semiconductors K22F series, Reference Manual, Page: 1299 / 1407

ET7816[RXTHRESHOLD] value will be incremented by one. However, if sufficient
space now exists to write the received data which was NACK'ed, S1[OR] will be blocked
and kept from asserting.
47.8.6 Match address registers
The two match address registers allow a second match address function for a broadcast or
general call address to the serial bus, as an example.
47.8.7 Modem feature
This section describes the modem features.
47.8.7.1 Ready-to-receive using RTS
To help to stop overrun of the receiver data buffer, the RTS signal can be used by the
receiver to indicate to another UART that it is ready to receive data. The other UART can
send the data when its CTS signal is asserted. This handshaking conforms to the
TIA-232-E standard. A transceiver is necessary if the required voltage levels of the
communication link do not match the voltage levels of the UART's RTS and CTS signals.
TRANSMITTER
UART
RECEIVER TRANSMITTER
UART
RECEIVER
TXD
CTS_B
RXD
RTS_B
RXD
RTS_B
TXD
CTS_B
Figure 47-28. Ready-to-receive
The transmitter's CTS signal can be used for hardware flow control whether its RTS
signal is used for hardware flow control, transceiver driver enable, or not at all.
47.8.7.2 Transceiver driver enable using RTS
RS-485 is a multiple drop communication protocol in which the UART transceiver's
driver is 3-stated unless the UART is driving. The RTS signal can be used by the
transmitter to enable the driver of a transceiver. The polarity of RTS can be matched to
the polarity of the transceiver's driver enable signal. See the following figure.
Chapter 47 Universal Asynchronous Receiver/Transmitter (UART)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 1299