Справочник Пользователя для Freescale Semiconductor Demonstration Board for Freescale MC9S12XHY256 Microcontroller DEMO9S12XHY256 DEMO9S12XHY256

Freescale Semiconductor

473

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).

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]