Transmitter
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
20-7
20.1.1 Character Transmission
To transmit data, one of the SC3400 cores or an external host writes the data character to the SCI
Data Register (SCIDR), which is then transferred to the transmitter shift register. The transmitter
shift register then shifts out the data bits on the
UTXD
signal, after it prefaces them with a start bit
and appends them with a stop bit. The SCI data register is the write-only buffer between the
MBus and the transmit shift register.
The UART also sets a flag, the transmit data register empty flag (TDRE), every time it transfers
data from the buffer (SCIDR) to the transmitter shift register. If the Transmit Interrupt Enable
(TIE) bit in the SCICR is set, the TDRE flag asserts a UART interrupt request. The transmit
interrupt service routine responds to this flag by writing another character to the transmitter
buffer (SCIDR), while the shift register is still shifting out the first character. If the TDRE flag is
set and no new data or break character transferred to the shift register, the UART sets a flag,
transmit complete (TC) and
UTXD
becomes idle.
Figure 20-6. Transmitter Block Diagram
PE
PT
H 8
7
6
5
4
3
2
1
0
L
11-Bit Transmit Shift Register
St
o
p
St
a
rt
T8
TDRE
TIE
TCIE
SBK
TC
Parity
Generation
MS
B
SCI Data Register T[7–0]
Lo
ad F
rom
S
C
IDR
S
h
if
t En
abl
e
Pr
e
a
mb
le (
A
ll O
nes
)
Br
e
a
k (A
ll
0s
)
M
SBR[12–0]
Baud-Rate
³ 16
UTXD
TDRE Interrupt Source
TC Interrupt Source
CLASS64 clock
Loop
LOOPS
RSRC
TE
To
Control
Receiver
Generator
Transmitter Control
MBus
Содержание MSC8144E
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