NXP Semiconductors MC9S08LG16, Справочное руководство

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Chapter 11 Serial Communications Interface (S08SCIV4)
MC9S08LG32 MCU Series, Rev. 5
264 Freescale Semiconductor
13.2 Register Definition
The SCI has eight 8-bit registers to control baud rate, select SCI options, report SCI status, and for
transmit/receive data.
Refer to the direct-page register summary in Chapter 4, “Memory ,” or the absolute address assignments
for all SCI registers. This section refers to registers and control bits only by their names. A
Freescale-provided equate or header file is used to translate these names into the appropriate absolute
addresses.
13.2.1 SCI Baud Rate Registers (SCIxBDH, SCIxBDL)
This pair of registers controls the prescale divisor for SCI baud rate generation. To update the 13-bit baud
rate setting [SBR12:SBR0], first write to SCIxBDH to buffer the high half of the new value and then write
to SCIxBDL. The working value in SCIxBDH does not change until SCIxBDL is written.
SCIxBDL is reset to a non-zero value, so after reset the baud rate generator remains disabled until the first
time the receiver or transmitter is enabled (RE or TE bits in SCIxC2 are written to 1).
7 6 5 4 3 2 1 0
R
LBKDIE RXEDGIE
0
SBR[12:8]
W
Reset 0 0 0 0 0 0 0 0
= Unimplemented or Reserved
Figure 13-4. SCI Baud Rate Register (SCIxBDH)
Table 13-2. SCIxBDH Field Descriptions
Field Description
7
LBKDIE
LIN Break Detect Interrupt Enable (for LBKDIF)
0 Hardware interrupts from LBKDIF disabled (use polling).
1 Hardware interrupt requested when LBKDIF flag is 1.
6
RXEDGIE
RxD Input Active Edge Interrupt Enable (for RXEDGIF)
0 Hardware interrupts from RXEDGIF disabled (use polling).
1 Hardware interrupt requested when RXEDGIF flag is 1.
4:0
SBR[12:8]
Baud Rate Modulo Divisor — The 13 bits in SBR[12:0] are referred to collectively as BR, and they set the
modulo divide rate for the SCI baud rate generator. When BR is cleared, the SCI baud rate generator is disabled
to reduce supply current. When BR is 1 – 8191, the SCI baud rate equals BUSCLK/(16
×
BR). See also BR bits
in Table 13-3 .