Datasheet

Chapter 13 Serial Communications Interface (S12SCIV2) Block Description
Freescale Semiconductor MC9S12C-Family / MC9S12GC-Family 387
Rev 01.24
13.3.2.1 SCI Baud Rate Registers (SCIBDH and SCHBDL)
The SCI Baud Rate Register is used by the counter to determine the baud rate of the SCI. The formula for
calculating the baud rate is:
SCI baud rate = SCI module clock / (16 x BR)
where:
BR is the content of the SCI baud rate registers, bits SBR12 through SBR0. The baud rate registers
can contain a value from 1 to 8191.
Read: Anytime. 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
Module Base + 0x_0000
76543210
R000
SBR12 SBR11 SBR10 SBR9 SBR8
W
Reset 0 0 0 00000
Module Base + 0x_0001
76543210
R
SBR7 SBR6 SBR5 SBR4 SBR3 SBR2 SBR1 SBR0
W
Reset 0 0 0 00100
= Unimplemented or Reserved
Figure 13-3. SCI Baud Rate Registers (SCIBDH and SCIBDL)
Table 13-1. SCIBDH AND SCIBDL Field Descriptions
Field Description
4–0
7–0
SBR[12:0]
SCI Baud Rate Bits — The baud rate for the SCI is determined by these 13 bits.
Note: The baud rate generator is disabled until the TE bit or the RE bit is set for the first time after reset. The
baud rate generator is disabled when BR = 0.
Writing to SCIBDH has no effect without writing to SCIBDL, since writing to SCIBDH puts the data in a
temporary location until SCIBDL is written to.