Transmitter
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
20-9
When the transmit shift register is not transmitting a character,
UTXD
goes to the idle condition,
logic 1. When software clears the SCICR[TE] bit, the transmitter relinquishes control of
UTXD
.
Note:
If SCIDDR[DDRTX] is set,
UTXD
is driven by a logic 0 (pulled down). Otherwise, if
SCIDDR[DDRTX] is cleared, the
UTXD
signal is not driven. See Chapter 22, GPIO
for details about configuring this signal.
If software clears SCICR[TE] while a transmission is in progress (TC = 0), the frame in the
transmit shift register continues to shift out. Then the transmitter relinquishes control of
UTXD
even if there is data pending in the SCI data register. To avoid accidentally cutting off the last
frame in a message, always wait for TDRE to go high after the last frame before clearing
SCICR[TE].
To separate messages with preambles with minimum idle line time, use the following sequence
between messages (see also Figure 20-7, Queuing an Idle Character):
1.
Write the last character of the first message to the SCIDR.
2.
Wait for the TDRE flag to go high, indicating the transfer of the last frame to the
transmit shift register.
3.
Insert a preamble by clearing and then setting the SCICR[TE] bit.
4.
Write the first character of the second message to the SCIDR.
Another way to separate messages with idle line is to wait until the TC flag is set after writing the
last character of the first message to SCIDR, indicating this character has already been
transmitted. When TC is set,
UTXD
goes idle. Then, after some idle line time, write the first
character of the second message to SCIDR.
20.1.2 Break Characters
Setting the send break bit (SCICR[SBK]) to a value of 1 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 is ten logic 0s (if M = 0) or eleven logic 0s (if M = 1). As long as SCICR[SBK] is at
logic 1, transmitter logic continuously loads break characters into the transmit shift register. After
software clears the SBK bit, 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 frame.
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...