K60P100M100SF2RM Datasheet, PDF (1525/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 51 Universal Asynchronous Receiver/Transmitter (UART)
51.4.1.2 Transmission bit order
When the S2[MSBF] bit is set, the UART automatically transmits the MSB of the data
word as the first bit after the start bit. Likewise the LSB of the data word is transmitted
immediately preceding the parity bit (or the stop bit if parity is not enabled). All
necessary bit ordering is handled automatically by the module hence the format of the
data written to the D register for transmission is completely independent of the
S2[MSBF] setting.
51.4.1.3 Character transmission
To transmit data, the MCU writes the data bits to the UART transmit buffer using UART
data registers (C3[T8]/D). Data in the transmit buffer is then in turn transferred to the
transmitter shift register as needed. The transmit shift register then shifts a frame out
through the transmit data output signal after it has prefaced it with any required start and
stop bits. The UART data registers (C3[T8] and D) provide access to the transmit buffer
structure.
The UART also sets a flag, the transmit data register empty flag (S1[TDRE]) and
generates interrupt or DMA request (C5[TDMAS]), whenever the number of datawords
in the transmit buffer is equal to or less than the value indicated by the
TWFIFO[TXWATER]. The transmit driver routine may respond to this flag by writing
additional datawords to the transmit buffer using (C3[T8]/D) as space permits.
See Application information for specific programing sequences.
Setting the C2[TE] bit automatically loads the transmit shift register with a preamble of
10 logic 1s (if C1[M] = 0), 11 logic 1s (if C1[M] = 1 and C4[M10] = 0), or 12 logic 1s (if
C1[M] = 1, C4[M10] = 1, C1[PE] = 1). After the preamble shifts out, control logic
transfers the data from the UART data register into the transmit shift register. The
transmitter automatically transmits the correct start bit and stop bit before and after the
dataword.
When C7816[ISO_7816E] = 1 setting the C2[TE] bit does not result in a preamble being
generated. The transmitter starts transmitting as soon as the corresponding guard time
expires. When C7816[TTYPE] = 0 the value in GT is used, when C7816[TTYPE] = 1 the
value BGT is used since it is assumed that the C2[TE] will remain asserted until the end
of the block transfer. The C2[TE] bit is automatically cleared when in C7816[TTYPE] =
1 and the block being transmitted has been completed. When C7816[TTYPE] = 0, the
transmitter listens for a NACK indication. If no NACK is received it is assumed that
character was correctly received. If a NACK is received the transmitter will resend the
data, assuming that the number of retries for that character (number of NACKs received)
is less than or equal to the value in ET7816[TXTHRESHOLD].
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1525