received. If a NACK is received, the transmitter resends the data, assuming that the
number of retries for that character, that is, the number of NACKs received, is less than
or equal to the value in ET7816[TXTHRESHOLD].
Hardware supports odd or even parity. When parity is enabled, the bit immediately
preceding the stop bit is the parity bit.
When the transmit shift register is not transmitting a frame, the transmit data output
signal goes to the idle condition, logic 1. If at any time software clears C2[TE], the
transmitter 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 the
transmit shift register continues to shift out, provided S1[TC] was cleared during the data
write sequence. To clear S1[TC], the S1 register must be read followed by a write to D
register.
If S1[TC] is cleared during character transmission and C2[TE] is cleared, the
transmission enable signal is deasserted at the completion of the current frame. Following
this, the transmit data out signal enters the idle state even if there is data pending in the
UART transmit data buffer. To ensure that all the data written in the FIFO is transmitted
on the link before clearing C2[TE], wait for S1[TC] to set. Alternatively, the same can be
achieved by setting TWFIFO[TXWATER] to 0x0 and waiting for S1[TDRE] to set.
46.4.1.4 Transmitting break characters
Setting C2[SBK] loads the transmit shift register with a break character. A break
character contains all logic 0s and has no start, stop, or parity bit. Break character length
depends on C1[M], C1[PE], S2[BRK13] and C4[M10]. See the following table.
Table 46-159. Transmit break character length
S2[BRK13]
C1[M]
C4[M10]
C1[PE]
Bits transmitted
0
0
—
—
10
0
1
1
0
11
0
1
1
1
12
1
0
—
—
13
1
1
—
—
14
As long as C2[SBK] is set, the transmitter logic continuously loads break characters into
the transmit shift register. After the software clears C2[SBK], the shift register finishes
transmitting the last break character and then transmits at least one logic 1. The automatic
logic 1 at the end of a break character guarantees the recognition of the start bit of the
next character. Break bits are not supported when C7816[ISO_7816E] is set/enabled.
Functional description
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
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Freescale Semiconductor, Inc.