MC9S12XD256MAL Datasheet, PDF (482/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Chapter 11 Serial Communication Interface (S12SCIV5)
11.3.2.1 SCI Baud Rate Registers (SCIBDH, SCIBDL)
R
W
Reset
7
IREN
0
6
TNP1
5
TNP0
4
SBR12
3
SBR11
2
SBR10
0
0
0
0
0
Figure 11-3. SCI Baud Rate Register (SCIBDH)
1
SBR9
0
0
SBR8
0
R
W
Reset
7
SBR7
0
6
SBR6
5
SBR5
4
SBR4
3
SBR3
2
SBR2
0
0
0
0
0
Figure 11-4. SCI Baud Rate Register (SCIBDL)
1
SBR1
0
0
SBR0
0
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.
Table 11-1. 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
Transmitter Narrow Pulse Bits — These bits enable whether the SCI transmits a 1/16, 3/16, 1/32 or 1/4 narrow
TNP[1:0] pulse. See Table 11-2.
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.
MC9S12XDP512 Data Sheet, Rev. 2.21
482
Freescale Semiconductor