STMicroelectronics STM32F407 User Manual

DocID018909 Rev 11 81/1731
RM0090 Embedded Flash memory interface
112
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.
Decreasing the CPU frequency
1. Modify the CPU clock source by writing the SW bits in the RCC_CFGR register
2. If needed, modify the CPU clock prescaler by writing the HPRE bits in RCC_CFGR
3. 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
4. Program the new number of wait states to the LATENCY bits in FLASH_ACR
5. Check that the new number of wait states is used to access the Flash memory by
reading the FLASH_ACR register
Table 11. Number of wait states according to CPU clock (HCLK) frequency
(STM32F42xxx and STM32F43xxx)
Wait states (WS)
(LATENCY)
HCLK (MHz)
Voltage range
2.7 V - 3.6 V
Voltage range
2.4 V - 2.7 V
Voltage range
2.1 V - 2.4 V
Voltage range
1.8 V - 2.1 V
Prefetch OFF
0 WS (1 CPU cycle) 0 <HCLK≤ 30 0 <HCLK ≤ 24 0 <HCLK ≤ 22 0 < HCLK ≤ 20
1 WS (2 CPU cycles) 30 <HCLK ≤ 60 24 < HCLK≤ 48 22 <HCLK ≤ 44 20 <HCLK ≤ 40
2 WS (3 CPU cycles) 60 <HCLK ≤ 90 48 < HCLK≤ 72 44 < HCLK≤ 66 40 < HCLK≤ 60
3 WS (4 CPU cycles) 90 <HCLK ≤ 120 72 < HCLK≤ 96 66 <HCLK ≤ 88 60 < HCLK≤ 80
4 WS (5 CPU cycles) 120 <HCLK ≤ 150 96 < HCLK≤ 120 88 < HCLK≤ 110 80 < HCLK≤ 100
5 WS (6 CPU cycles) 150 <HCLK ≤ 180 120 <HCLK ≤ 144 110 < HCLK≤ 132 100 < HCLK≤ 120
6 WS (7 CPU cycles)
144 <HCLK ≤ 168 132 < HCLK≤ 154 120 < HCLK≤ 140
7 WS (8 CPU cycles)
168 <HCLK ≤ 180 154 <HCLK ≤ 176 140 < HCLK≤ 160
8 WS (9 CPU cycles)
176 <HCLK ≤ 180 160 < HCLK≤ 168

STMicroelectronics STM32F407 Specifications

General

Brand	STMicroelectronics
Model	STM32F407
Category	Controller
Language	English