RM0440 Rev 4 291/2126
RM0440 Reset and clock control (RCC)
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7.4.3 Clock configuration register (RCC_CFGR)
Address offset: 0x08
Reset value: 0x0000 0005
Access: 0 ≤ wait state ≤ 2, word, half-word and byte access
1 or 2 wait states inserted only if the access occurs during clock source switch.
From 0 to 15 wait states inserted if the access occurs when the APB or AHB prescalers
values update is on going.
Bit 31 Reserved, must be kept at reset value.
Bits 30:24 HSITRIM[6:0]: HSI16 clock trimming
These bits provide an additional user-programmable trimming value that is added to the
HSICAL[7:0] bits. It can be programmed to adjust to variations in voltage and temperature
that influence the frequency of the HSI16.
The default value is 16, which, when added to the HSICAL value, should trim the HSI16 to
16 MHz ± 1 %.
Bits 23:16 HSICAL[7:0]: HSI16 clock calibration
These bits are initialized at startup with the factory-programmed HSI16 calibration trim value.
When HSITRIM is written, HSICAL is updated with the sum of HSITRIM and the factory trim
value.
Bits 15:0 Reserved, must be kept at reset value.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Res. MCOPRE[2:0] MCOSEL[3:0] Res. Res. Res. Res. Res. Res. Res. Res.
rw rw rw rw rw rw rw
1514131211109 8 7 65432 1 0
Res. Res. PPRE2[2:0] PPRE1[2:0] HPRE[3:0] SWS[1:0] SW[1:0]
rw rw rw rw rw rw rw rw rw rw r r rw rw
Bit 31 Reserved, must be kept at reset value.
Bits 30:28 MCOPRE[2:0]: Microcontroller clock output prescaler
These bits are set and cleared by software.
It is highly recommended to change this prescaler before MCO output is enabled.
000: MCO is divided by 1
001: MCO is divided by 2
010: MCO is divided by 4
011: MCO is divided by 8
100: MCO is divided by 16
Others: not allowed
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