3. Repeat step 2 for each subsequent transmission.
Note
During normal operation, S1[TDRE] 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]. This 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 S1[TDRE] 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 C2[TE].
4. Write the first and subsequent datawords of the second message to C3[T8]/D.
46.8.3 Overrun (OR) flag implications
To be flexible, the overrun flag (OR) operates slight differently depending on the mode
of operation. There may be implications that need to be carefully considered. This section
clarifies the behavior and the resulting implications. Regardless of mode, if a dataword is
received while S1[OR] is set, S1[RDRF] and S1[IDLE] are blocked from asserting. If
S1[RDRF] or S1[IDLE] were previously asserted, they will remain asserted until cleared.
46.8.3.1 Overrun operation
The assertion of S1[OR] indicates that a significant event has occurred. The assertion
indicates that received data has been lost because there was a lack of room to store it in
the data buffer. Therefore, while S1[OR] is set, no further data is stored in the data buffer
until S1[OR] is cleared. This ensures that the application will be able to handle the
overrun condition.
In most applications, because the total amount of lost data is known, the application will
attempt to return the system to a known state. Before S1[OR] is cleared, all received data
will be dropped. For this, the software does the following.
Chapter 46 Universal Asynchronous Receiver/Transmitter (UART)
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
Freescale Semiconductor, Inc.
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