Reset, Clock, and Power Controller
LH79524/LH79525 User’s Guide
13-18
Version 1.0
13.2.2.8 CPU Clock Prescaler Register (CPUCLKPRE)
FCLK is the CPU Clock. This register allows a divisor to be programmed that is used to
divide the system PLL frequency to derive FCLK. The prescaled FCLK frequency is
defined by:
Following reset, the prescaler is programmed to divide by 30. Table 13-21 shows example
values for FDIV. The CPU clock must always be greater than or equal to the system bus
clock. Thus when changing clock dividers, the CPU frequency should be increased
BEFORE, decreased AFTER, and always kept at least equal to the system bus frequency.
Table 13-19. CPUCLKPRE Register
BIT
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
FIELD
///
RESET
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
RW
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
BIT
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
FIELD
///
FDIV
RESET
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
RW
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RW
RW
RW
RW
ADDR
0xFF 0x1C
Table 13-20. CPUCLKPRE Fields
BITS
NAME
DESCRIPTION
31:4
///
Reserved
Reading returns 0. Write the reset value.
3:0
FDIV
FCLK Divisor
Program with the divisor for the HCLK prescaler. All FDIV
combinations are valid except 0b0000.
Table 13-21. CPUCLKPRE Register Values
FDIV
DIVISOR VALUE
ƒ(FCLK)
0b0000
—
Invalid
0b0001
2
ƒ(System PLL)/2
0b0010
4
ƒ(System PLL)/4
0b0011
6
ƒ(System PLL)/6
0b0100
8
ƒ(System PLL)/8
0b0101
10
ƒ(System PLL)/10
:
:
:
0b1111 (default)
30
ƒ(System PLL)/30
ƒ(FCLK)
ƒ
ƒ(SystemPLL)
2
FDIV
×
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