MC68HC908GR8 Datasheet, PDF (184/286 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Serial Communications Interface (SCI)
SCP1 and SCP0 — SCI Baud Rate Prescaler Bits
These read/write bits select the baud rate prescaler divisor as shown in Table 18-6. Reset clears SCP1
and SCP0.
Table 18-6. SCI Baud Rate Prescaling
SCP1 and SCP0
00
01
10
11
Prescaler Divisor (PD)
1
3
4
13
SCR2–SCR0 — SCI Baud Rate Select Bits
These read/write bits select the SCI baud rate divisor as shown in Table 18-7. Reset clears
SCR2–SCR0.
Table 18-7. SCI Baud Rate Selection
SCR2, SCR1, and SCR0
000
001
010
011
100
101
110
111
Baud Rate Divisor (BD)
1
2
4
8
16
32
64
128
Use this formula to calculate the SCI baud rate:
baud rate = -----------f--B----U-----S--------------
64 × PD × BD
where:
f_BUS = bus frequency
PD = prescaler divisor
BD = baud rate divisor
SCIBDSRC from the configuration register is an input to the SCI. With SCIBDSRC = 1 to select the bus
clock as the clock source, this makes the formula:
baud rate = -----------f--B----U----S---------------
64 × PD × BD
Table 18-8 shows the SCI baud rates that can be generated with a 4.9152-MHz bus clock.
MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7
184
Freescale Semiconductor