Freescale Semiconductor, Inc.
Clock Functions
the transition, the clock select output will be held low and all CPU activity
will cease until the transition is complete.
The Module Clock Select bit MCS determines the clock used by the ECT
module and the baud rate generators of the SCIs. In limp-home mode,
the output of MCS is forced to 0, but the MCS bit reads the latched value.
It allows normal operation of the serial and timer subsystems at a fixed
reference frequency while allowing the CPU to operate at a higher,
variable frequency.
XCLK
÷ 2048
÷4
0:0:0
0:0:0
REGISTER: COPCTL
BITS: CR2, CR1, CR0
REGISTER: RTICTL
BITS: RTR2, RTR1, RTR0
REGISTER: RTICTL
BIT:RTBYP
0:0:1
0:1:0
0:0:1
0:1:0
÷ 2
÷ 4
÷ 4
÷ 4
÷ 4
÷ 2
÷ 2
SC0BD
MODULUS DIVIDER:
÷ 1, 2, 3, 4, 5, 6,...,8190, 8191
SCI0
RECEIVE
BAUD RATE (16x)
÷ 2
0:1:1
0:1:1
MCLK
÷ 2
÷ 2
÷ 2
÷ 2
1:0:0
1:0:1
1:1:0
1:1:1
1:0:0
1:0:1
1:1:0
1:1:1
÷ 16
SCI0
TRANSMIT
BAUD RATE (1x)
SC1BD
MODULUS DIVIDER:
÷ 1, 2, 3, 4, 5, 6,...,8190, 8191
SCI1
RECEIVE
BAUD RATE (16x)
÷ 16
SCI1
TRANSMIT
BAUD RATE (1x)
TO RTI
TO COP
Figure 12-7. Clock Chain for SCI0, SCI1, RTI, COP
Advance Information
170
68HC(9)12D60 — Rev 4.0
MOTOROLA
Clock Functions
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