DocID018909 Rev 11
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RM0090
Reset and clock control for STM32F42xxx and STM32F43xxx (RCC)
212
6.3.25
RCC Dedicated Clock Configuration Register (RCC_DCKCFGR)
Address offset: 0x8C
Reset value: 0x0000 0000
Access: no wait state, word, half-word and byte access.
The RCC_DCKCFGR register allows to configure the timer clock prescalers and the PLLSAI
and PLLI2S output clock dividers for SAI1 and LTDC peripherals according to the following
formula:
f
(PLLSAIDIVQ clock output)
= f
(PLLSAI_Q)
/ PLLSAIDIVQ
f
(PLLSAIDIVR clock output)
= f
(PLLSAI_R)
/ PLLSAIDIVR
f(
PLLI2SDIVQ clock output)
= f
(PLLI2S_Q)
/ PLLI2SDIVQ
Bits 23:15 Reserved, must be kept at reset value.
Bits 14:6
PLLSAIN:
PLLSAI division factor for VCO
These bits are set and cleared by software to control the multiplication factor of the VCO.
These bits can be written only when PLLSAI is disabled. Only half-word and word accesses
are allowed to write these bits.
Caution:
The software has to set these bits correctly to ensure that the VCO output frequency
is between 100 and 432 MHz.
VCO output frequency = VCO input frequency × PLLISAIN with 50
≤
PLLISAIN
≤
432
000000000: PLLISAIN = 0, wrong configuration
000000001: PLLISAIN = 1, wrong configuration
...
000110010: PLLISAIN = 50
...
001100011: PLLISAIN = 99
001100100: PLLISAIN = 100
001100101: PLLISAIN = 101
001100110: PLLISAIN = 102
...
110110000: PLLISAIN = 432
110110001: PLLISAIN = 433, wrong configuration
...
111111111: PLLISAIN = 511, wrong configuration
Note: Multiplication factors ranging from 50 and 99 are possible for VCO input frequency
higher than 1 MHz. However care must be taken that the minimum VCO output
frequency respects the value specified above.
Bits 5:0 Reserved, must be kept at reset value
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
Reserved
TIMPRE
SAI1BSRC
SAI1ASRC
Reserved
PLLSAIDIVR
rw
rw
rw
rw
rw
rw
rw
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Reserved
PLLSAIDIVQ
Reserved
PLLS2DIVQ
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw