Number Of Wait States According To Cpu Clock (Hclk) Frequency - ST STM32F40 Series Reference Manual

RM0090
Note: On STM32F405xx/07xx and STM32F415xx/17xx devices:
- when VOS = '0', the maximum value of f
- when VOS = '1', the maximum value of f
On STM32F42xxx and STM32F43xxx devices:
- when VOS[1:0] = '0x01', the maximum value of f
- when VOS[1:0] = '0x10', the maximum value of f
- when VOS[1:0] = '0x11', the maximum value of f
Table 7.

Number of wait states according to CPU clock (HCLK) frequency

Wait states (WS)
(LATENCY)
0 WS (1 CPU cycle)
1 WS (2 CPU cycles)
2 WS (3 CPU cycles)
3 WS (4 CPU cycles)
4 WS (5 CPU cycles)
5 WS (6 CPU cycles)
6 WS (7 CPU cycles)
7 WS (8 CPU cycles)
After reset, the CPU clock frequency is 16 MHz and 0 wait state (WS) is configured in the
FLASH_ACR register.
It is highly recommended to use the following software sequences to tune the number of
wait states needed to access the Flash memory with the CPU frequency.
Increasing the CPU frequency
1. Program the new number of wait states to the LATENCY bits in the FLASH_ACR
register
2. Check that the new number of wait states is taken into account to access the Flash
memory by reading the FLASH_ACR register
3. Modify the CPU clock source by writing the SW bits in the RCC_CFGR register
4. If needed, modify the CPU clock prescaler by writing the HPRE bits in RCC_CFGR
5. Check that the new CPU clock source or/and the new CPU clock prescaler value is/are
taken into account by reading the clock source status (SWS bits) or/and the AHB
prescaler value (HPRE bits), respectively, in the RCC_CFGR register.
Voltage range
2.7 V - 3.6 V
0 < HCLK≤ 30
30 < HCLK ≤ 60
60 < HCLK ≤ 90
90 < HCLK ≤ 120
120 < HCLK ≤ 150
150 < HCLK ≤ 168 120 < HCLK ≤ 144
144 < HCLK ≤ 168
Doc ID 018909 Rev 4
Embedded Flash memory interface
= 144 MHz.
HCLK
= 168 MHz.
HCLK
HCLK
HCLK
HCLK
HCLK (MHz)
Voltage range Voltage range
2.4 V - 2.7 V
0 < HCLK ≤ 24 0 < HCLK ≤ 22
22 < HCLK ≤ 44
24 < HCLK≤ 48
48 < HCLK≤ 72 44 < HCLK≤ 66
66 < HCLK ≤ 88
72 < HCLK≤ 96
96 < HCLK≤ 120 88 < HCLK≤ 110
110 < HCLK≤ 132
132 < HCLK≤ 154
154 < HCLK ≤ 168
is 120 MHz.
is 144 MHz.
is 168 MHz
Voltage range
1.8 V - 2.1 V
2.1 V - 2.4 V
Prefetch OFF
0 < HCLK ≤ 20
20 <HCLK ≤ 40
40 < HCLK≤ 60
60 < HCLK≤ 80
80 < HCLK≤ 100
100 < HCLK≤ 120
120 < HCLK≤ 140
140 < HCLK≤ 160
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