NXP Semiconductors Kinetis KE1xZ256, Reference Manual

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46.3.1.13.4 Fields
Field Function
31-24
RXCOUNT
Receive Counter
The value in this register indicates the number of datawords that are in the receive FIFO/buffer. If a
dataword is being received, that is, in the receive shift register, it is not included in the count. This value
may be used in conjunction with FIFO[RXFIFOSIZE] to calculate how much room is left in the receive
FIFO/buffer.
23-16
RXWATER
Receive Watermark
When the number of datawords in the receive FIFO/buffer is greater than the value in this register field,
an interrupt or a DMA request is generated. For proper operation, the value in RXWATER must be set to
be less than the receive FIFO/buffer size as indicated by FIFO[RXFIFOSIZE] and FIFO[RXFE] and must
be greater than 0.
15-8
TXCOUNT
Transmit Counter
The value in this register indicates the number of datawords that are in the transmit FIFO/buffer. If a
dataword is being transmitted, that is, in the transmit shift register, it is not included in the count. This
value may be used in conjunction with FIFO[TXFIFOSIZE] to calculate how much room is left in the
transmit FIFO/buffer.
7-0
TXWATER
Transmit Watermark
When the number of datawords in the transmit FIFO/buffer is equal to or less than the value in this
register field, an interrupt or a DMA request is generated. For proper operation, the value in TXWATER
must be set to be less than the size of the transmit buffer/FIFO size as indicated by FIFO[TXFIFOSIZE]
and FIFO[TXFE].
46.4 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.
46.4.1 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.
Chapter 46 Low Power Universal Asynchronous Receiver/Transmitter (LPUART)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors 1205