K60P100M100SF2RM Datasheet, PDF (1561/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 51 Universal Asynchronous Receiver/Transmitter (UART)
b. If the TDRE flag is set, or there is space in the transmit buffer, write the data to
be transmitted to (C3[T8]/D). A new transmission will not result until data exists
in the transmit buffer.
3. Repeat step 2 for each subsequent transmission.
Note
During normal operation, the S1[TDRE] flag is set when the
shift register is loaded with the next data to be transmitted from
the transmit buffer and the number of datawords contained in
the transmit buffer is less than or equal to the value in
TWFIFO[TXWATER], which occurs 9/16ths of a bit time after
the start of the stop bit of the previous frame.
To separate messages with preambles with minimum idle line time, use this sequence
between messages:
1. Write the last dataword of the first message to C3[T8]/D.
2. Wait for the S1[TDRE] flag to go high (with TWFIFO[TXWATER] = 0), indicating
the transfer of the last frame to the transmit shift register.
3. Queue a preamble by clearing and then setting the C2[TE] bit.
4. Write the first (and subsequent) datawords of the second message to C3[T8]/D.
51.8.4 Overrun (OR) flag implications
To be flexible the overrun flag (OR) operates slight differently depending on the mode of
operation. As such there may be implications that need to be carefully considered. This
section clarifies that behavior and the resulting implications. Regardless of mode, if a
dataword is received while the S1[OR] flag is set, the S1[RDRF] and S1[IDLE] flags are
blocked from asserting. If the S1[RDRF] or S1[IDLE] flag were previously asserted they
will remain asserted until cleared.
51.8.4.1 Overrun operation
The assertion of the S1[OR] flag indicates that a significant event has occurred. The
assertion indicates that received data has been lost since there was a lack of room to store
it in the data buffer. Hence, while the S1[OR] flag is set no further data will be stored in
the data buffer until the S1[OR] flag is cleared. This ensures that the application will be
able to handle the overrun condition.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1561