Serial Communication Interface (S12SCIV5)
11.4.5 Transmitter
Internal Bus
Bus
÷ 16
Baud Divider
Clock
SCI Data Registers
SBR12:SBR0
TXPOL
SCTXD
11-Bit Transmit Register
H
8
7
6
5
4
3
2
1
0
L
M
LOOP
CONTROL
To Receiver
T8
PE
PT
Parity
Generation
LOOPS
RSRC
TIE
TDRE IRQ
TC IRQ
TDRE
Transmitter Control
TC
TCIE
TE
SBK
BERRM[1:0]
SCTXD
BERRIF
TCIE
Transmit
Collision Detect
BER IRQ
SCRXD
(From Receiver)
Figure 11-16. Transmitter Block Diagram
11.4.5.1 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).
11.4.5.2 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.
S12P-Family Reference Manual, Rev. 1.13
Freescale Semiconductor
381
FREESCALE [ Freescale ]
