LPUARTx_MODIR field descriptions (continued)
Field
Description
0
The transmitter has no effect on RTS.
1
When a character is placed into an empty transmitter data buffer , RTS asserts one bit time before the
start bit is transmitted. RTS deasserts one bit time after all characters in the transmitter data buffer
and shift register are completely sent, including the last stop bit.
0
TXCTSE
Transmitter clear-to-send enable
TXCTSE controls the operation of the transmitter. TXCTSE can be set independently from the state of
TXRTSE and RXRTSE.
0
CTS has no effect on the transmitter.
1
Enables clear-to-send operation. The transmitter checks the state of CTS each time it is ready to send
a character. If CTS is asserted, the character is sent. If CTS is deasserted, the signal TXD remains in
the mark state and transmission is delayed until CTS is asserted. Changes in CTS as a character is
being sent do not affect its transmission.
47.3 Functional description
The LPUART supports full-duplex, asynchronous, NRZ serial communication and
comprises a baud rate generator, transmitter, and receiver block. The transmitter and
receiver operate independently, although they use the same baud rate generator. The
following describes each of the blocks of the LPUART.
47.3.1 Baud rate generation
A 13-bit modulus counter in the baud rate generator derive the baud rate for both the
receiver and the transmitter. The value from 1 to 8191 written to SBR[12:0] determines
the baud clock divisor for the asynchronous LPUART baud clock. The SBR bits are in
the LPUART baud rate registers, BDH and BDL. The baud rate clock drives the receiver,
while the transmitter is driven by the baud rate clock divided by the over sampling ratio.
Depending on the over sampling ratio, the receiver has an acquisition rate of 4 to 32
samples per bit time.
Functional description
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
1236
Freescale Semiconductor, Inc.
