Chapter 15 Serial Communication Interface (S12MC9S12XDP512V5)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 697
15.4.6 Receiver
Figure 15-20. SCI Receiver Block Diagram

15.4.6.1 Receiver Character Length

The SCI receiver 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 receiving 9-bit data, bit R8 in

SCI data register high (SCIDRH) is the ninth bit (bit 8).

15.4.6.2 Character Reception

During an SCI reception, the receive shift register shifts a frame in from the RXD pin. The SCI data register

is the read-only buffer between the internal data bus and the receive shift register.

After a complete frame shifts into the receive shift register, the data portion of the frame transfers to the

SCI data register. The receive data register full flag, RDRF, in SCI status register 1 (SCISR1) becomes set,

All 1s
M
WAKE
ILT
PE
PT
RE
H876543210L
11-Bit Receive Shift Register
Stop
Start
Data
Wakeup
Parity
Checking
MSB
SCI Data Register
R8
ILIE
RWU
RDRF
OR
NF
FE
PE
Internal Bus
Bus
SBR12:SBR0
Baud Divider
Clock
IDLE
RAF
Recovery
Logic
RXPOL
LOOPS
Loop
RSRC
Control
SCRXD
From TXD Pin
or Transmitter
Idle IRQ
RDRF/OR
IRQ
Break
Detect Logic
Active Edge
Detect Logic
BRKDFE
BRKDIE
BRKDIF
RXEDGIE
RXEDGIF
Break IRQ
RX Active Edge IRQ
RIE