Chapter 20 Serial Communication Interface (S12SCIV5)
MC9S12XE-Family Reference Manual , Rev. 1.19
742
Freescale Semiconductor
20.4.5
Transmitter
Figure 20-16. Transmitter Block Diagram
20.4.5.1
Transmitter Character Length
The SCI transmitter can accommodate either 8-bit or 9-bit data characters. The state of the M bit in SCI
control register 1 (SCICR1) determines the length of data characters. When transmitting 9-bit data, bit T8
in SCI data register high (SCIDRH) is the ninth bit (bit 8).
20.4.5.2
Character Transmission
To transmit data, the MCU writes the data bits to the SCI data registers (SCIDRH/SCIDRL), which in turn
are transferred to the transmitter shift register. The transmit shift register then shifts a frame out through
the TXD pin, after it has prefaced them with a start bit and appended them with a stop bit. The SCI data
registers (SCIDRH and SCIDRL) are the write-only buffers between the internal data bus and the transmit
shift register.
PE
PT
H
8
7
6
5
4
3
2
1
0
L
11-Bit Transmit Register
Stop
Star
t
T8
TIE
TDRE
TCIE
SBK
TC
Parity
Generation
MSB
SCI Data Registers
Load from SCIDR
Shift Enab
le
Preamb
le (All 1s)
Break (All 0s)
Transmitter Control
M
Internal Bus
SBR12:SBR0
Baud Divider
÷
16
Bus
Clock
TE
SCTXD
TXPOL
LOOPS
LOOP
RSRC
CONTROL
To Receiver
Transmit
Collision Detect
TDRE IRQ
TC IRQ
SCTXD
SCRXD
(From Receiver)
TCIE
BERRIF
BER IRQ
BERRM[1:0]
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages