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Chapter 15 Serial Communication Interface (S12MC9S12XDP512V5)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 677
15.3.2.1 SCI Baud Rate Registers (SCIBDH, SCIBDL)
Read: Anytime, if AMAP = 0. If only SCIBDH is written to, a read will not return the correct data until
SCIBDL is written to as well, following a write to SCIBDH.
Write: Anytime, if AMAP = 0.
NOTE
Those two registers are only visible in the memory map if AMAP = 0 (reset
condition).
The SCI baud rate register is used by to determine the baud rate of the SCI, and to control the infrared
modulation/demodulation submodule.
Module Base + 0x0000
76543210
R
IREN TNP1 TNP0 SBR12 SBR11 SBR10 SBR9 SBR8
W
Reset 00000000
Figure 15-3. SCI Baud Rate Register (SCIBDH)
Module Base + 0x0001
76543210
R
SBR7 SBR6 SBR5 SBR4 SBR3 SBR2 SBR1 SBR0
W
Reset 00000000
Figure 15-4. SCI Baud Rate Register (SCIBDL)
Table 15-2. SCIBDH and SCIBDL Field Descriptions
Field Description
7
IREN
Infrared Enable Bit — This bit enables/disables the infrared modulation/demodulation submodule.
0 IR disabled
1 IR enabled
6:5
TNP[1:0]
Transmitter Narrow Pulse Bits — These bits enable whether the SCI transmits a 1/16, 3/16, 1/32 or 1/4 narrow
pulse. See Table 15-3.
4:0
7:0
SBR[12:0]
SCI Baud Rate Bits — The baud rate for the SCI is determined by the bits in this register. The baud rate is
calculated two different ways depending on the state of the IREN bit.
The formulas for calculating the baud rate are:
When IREN = 0 then,
SCI baud rate = SCI bus clock / (16 x SBR[12:0])
When IREN = 1 then,
SCI baud rate = SCI bus clock / (32 x SBR[12:1])
Note: The baud rate generator is disabled after reset and not started until the TE bit or the RE bit is set for the
first time. The baud rate generator is disabled when (SBR[12:0] = 0 and IREN = 0) or (SBR[12:1] = 0 and
IREN = 1).
Note: Writing to SCIBDH has no effect without writing to SCIBDL, because writing to SCIBDH puts the data in
a temporary location until SCIBDL is written to.