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2. Transmit procedure for each byte.
a. Monitor S1[TDRE] by reading S1 or responding to the TDRE interrupt. The
amount of free space in the transmit buffer directly using TCFIFO[TXCOUNT]
can also be monitored.
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.
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.
46.9.3 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.
Freescale Semiconductor, Inc.
Chapter 46 Universal Asynchronous Receiver/Transmitter (UART) / FlexSCI
Note
KV4x Reference Manual, Rev. 2, 02/2015
Preliminary
1323
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