1. Configure the UART.a. Select a baud rate. Write this value to the UART baud registers (BDH/L) tobegin the baud rate generator. Remember that the baud rate generator is disabledwhen the baud rate is zero. Writing to the BDH has no effect without alsowriting to BDL.b. Write to C1 to configure word length, parity, and other configuration bits(LOOPS, RSRC, M, WAKE, ILT, PE, and PT). Write to C4, MA1, and MA2 toconfigure.c. Enable the transmitter, interrupts, receiver, and wakeup as required, by writing toC2 (TIE, TCIE, RIE, ILIE, TE, RE, RWU, and SBK), S2 (MSBF and BRK13),and C3 (ORIE, NEIE, PEIE, and FEIE). A preamble or idle character is thenshifted out of the transmitter shift register.2. Transmit procedure for each byte.a. Monitor S1[TDRE] by reading S1 or responding to the TDRE interrupt.b. If the TDRE flag is set, or there is space in the transmit buffer, write the data tobe transmitted to (C3[T8]/D). A new transmission will not result until data existsin the transmit buffer.3. Repeat step 2 for each subsequent transmission.NoteDuring normal operation, S1[TDRE] is set when the shiftregister is loaded with the next data to be transmitted from thetransmit buffer. This occurs 9/16ths of a bit time after the startof the stop bit of the previous frame.To separate messages with preambles with minimum idle line time, use this sequencebetween messages.1. Write the last dataword of the first message to C3[T8]/D.2. Wait for S1[TDRE] to go high, indicating the transfer of the last frame to thetransmit 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.Application informationKL27 Sub-Family Reference Manual , Rev. 5, 01/2016740 Freescale Semiconductor, Inc.
