PC912XDP512F0MPVR datasheet(482/1348 Pages) FREESCALE

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Chapter 11 Serial Communication Interface (S12SCIV5)

MC9S12XDP512 Data Sheet, Rev. 2.21

482

Freescale Semiconductor

11.3.2.1

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.

76543210

IREN

TNP1

TNP0

SBR12

SBR11

SBR10

SBR9

SBR8

Reset

00000000

Figure 11-3. SCI Baud Rate Register (SCIBDH)

76543210

SBR7

SBR6

SBR5

SBR4

SBR3

SBR2

SBR1

SBR0

Reset

00000000

Figure 11-4. SCI Baud Rate Register (SCIBDL)

Table 11-1. SCIBDH and SCIBDL Field Descriptions

Field

Description

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 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.

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