Chapter 15 Serial Communication Interface (S12MC9S12XDP512V5)
MC9S12XDP512 Data Sheet, Rev. 2.11
692 Freescale Semiconductor
15.4.5 Transmitter
Figure 15-16. Transmitter Block Diagram

15.4.5.1 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).

15.4.5.2 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
H876543210L
11-Bit Transmit Register
Stop
Start
T8
TIE
TDRE
TCIE
SBK
TC
Parity
Generation
MSB
SCI Data Registers
Load from SCIDR
Shift Enable
Preamble (All 1s)
Break (All 0s)
Transmitter Control
M
Internal Bus
SBR12:SBR0
Baud Divider รท16
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]