Serial Communications Interface Module (SCI)
11.8.7 SCI Baud Rate Register
The baud rate register (SCBR) selects the baud rate for both the receiver and the transmitter.
Address:
Read:
$0019
0
6
0
5
SCP1
0
4
SCP0
0
3
2
1
SCR1
0
Bit 0
SCR0
0
R
SCR2
Write:
Reset:
0
0
0
0
= Unimplemented
R
= Reserved
Figure 11-16. SCI Baud Rate Register (SCBR)
SCP1 and SCP0 — SCI Baud Rate Prescaler Bits
These read/write bits select the baud rate prescaler divisor as shown in Table 11-6. Reset clears SCP1
and SCP0.
Table 11-6. SCI Baud Rate Prescaling
SCP1 and SCP0
Prescaler Divisor (PD)
00
01
10
11
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 11-7. Reset clears
SCR2–SCR0.
Table 11-7. SCI Baud Rate Selection
SCR2, SCR1, and SCR0
Baud Rate Divisor (BD)
000
001
010
011
100
101
110
111
1
2
4
8
16
32
64
128
Use this formula to calculate the SCI baud rate:
SCI clock source
baud rate = --------------------------------------------
64 × PD × BD
where:
SCI clock source = f
or CGMXCLK
BUS
(selected by SCIBDSRC bit in CONFIG2 register)
PD = prescaler divisor
BD = baud rate divisor
MC68HC908AP Family Data Sheet, Rev. 4
178
Freescale Semiconductor
FREESCALE [ Freescale ]
