received. If a NACK is received, the transmitter resends the data, assuming that thenumber of retries for that character, that is, the number of NACKs received, is less thanor equal to the value in ET7816[TXTHRESHOLD].Hardware supports odd or even parity. When parity is enabled, the bit immediatelypreceding the stop bit is the parity bit.When the transmit shift register is not transmitting a frame, the transmit data outputsignal goes to the idle condition, logic 1. If at any time software clears C2[TE], thetransmitter enable signal goes low and the transmit signal goes idle.If the software clears C2[TE] while a transmission is in progress, the character in thetransmit shift register continues to shift out, provided S1[TC] was cleared during the datawrite sequence. To clear S1[TC], the S1 register must be read followed by a write to Dregister.If S1[TC] is cleared during character transmission and C2[TE] is cleared, thetransmission enable signal is deasserted at the completion of the current frame. Followingthis, the transmit data out signal enters the idle state even if there is data pending in theUART transmit data buffer.38.5.1.4 Transmitting break charactersSetting C2[SBK] loads the transmit shift register with a break character. A breakcharacter contains all logic 0s and has no start, stop, or parity bit. Break character lengthdepends on C1[M], C1[PE], S2[BRK13] and C4[M10]. See the following table.Table 38-3. Transmit break character lengthS2[BRK13] C1[M] C4[M10] C1[PE] Bits transmitted0 0 — — 100 1 1 0 110 1 1 1 121 0 — — 131 1 — — 14As long as C2[SBK] is set, the transmitter logic continuously loads break characters intothe transmit shift register. After the software clears C2[SBK], the shift register finishestransmitting the last break character and then transmits at least one logic 1. The automaticlogic 1 at the end of a break character guarantees the recognition of the start bit of thenext character. Break bits are not supported when C7816[ISO_7816E] is set/enabled.Chapter 38 Universal Asynchronous Receiver/Transmitter(UART)KL27 Sub-Family Reference Manual , Rev. 5, 01/2016Freescale Semiconductor, Inc. 711
