Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
5.8.1 SCBDH, SCBDL — SCI baud rate control registers
State
on reset
Address bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
SCI 1 baud rate high (SCBDH) $0070 BTST BSPL
0
SBR12 SBR11 SBR10 SBR9 SBR8 0000 0000
SCI 1 baud rate low (SCBDL) $0071 SBR7 SBR6 SBR5 SBR4 SBR3 SBR2 SBR1 SBR0 0000 0100
The contents of this register determine the baud rate of the SCI.
BTST — Baud register test (Test mode only)
BSPL — Baud rate counter split (Test mode only)
Bit 5 — Not implemented; always reads zero
SBR[12:0] — SCI baud rate selects
Use the following formula to calculate SCI baud rate. Refer to the
table of baud rate control values for example rates:
ST4XCK
SCI baud rate = ----------------------------
16 × (2BR)
where the baud rate control value (BR) is the contents of SCBDH/L
(BR = 1, 2, 3,... 8191).
BR = 0 disables the baud rate generator. For example, to obtain a
baud rate of 1200 with a 12MHz crystal, the baud register (SCBDH/L)
should contain $0138 (see Table 5-1).
NOTE: ST4XCK may be the output of the PLL circuit or it may be the EXTAL
input of the MCU. Selection is made by the MCS bit in the PLLCR (see
Crystal driver and external clock input (XTAL, EXTAL)).
Technical Data
MC68HC11P2 — Rev 1.0
Serial Communications Interface (SCI)
For More Information On This Product,
Go to: www.freescale.com
FREESCALE [ Freescale ]
