mc9s12ne64 Freescale Semiconductor, Inc, mc9s12ne64 Datasheet - Page 246

• Manufacturer Part Number: mc9s12ne64
• Description: Hcs12 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 8 Serial Communication Interface (SCIV3)
8.4.4
8.4.4.1
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).
8.4.4.2
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.
The SCI also sets a flag, the transmit data register empty flag (TDRE), every time it transfers data from
the buffer (SCIDRH/L) to the transmitter shift register. The transmit driver routine may respond to this
246
TDRE INTERRUPT REQUEST
CLOCK
BUS
TC INTERRUPT REQUEST
SBR12–SBR0
Transmitter
Transmitter Character Length
Character Transmission
BAUD DIVIDER
PE
PT
M
GENERATION
PARITY
÷
T8
16
Figure 8-13. Transmitter Block Diagram
MC9S12NE64 Data Sheet, Rev. 1.1
H
11-BIT TRANSMIT SHIFT REGISTER
8
TDRE
TCIE
TIE
TC
7
6
SCI DATA REGISTERS
5
TRANSMITTER CONTROL
INTERNAL BUS
4
3
2
TE
1
0
SBK
L
CONTROL
LOOP
Freescale Semiconductor
LOOPS
RSRC
TO RECEIVER
SCTXD