STM8AF526X datasheet(17/125 Pages) STMICROELECTRONICS

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STM8AF526x/8x/Ax STM8AF6269/8x/Ax

Product overview

114

The ROP circuit may provide a temporary access for debugging or failure analysis. The

temporary read access is protected by a user defined, 8-byte keyword stored in the option

byte area. This keyword must be entered via the SWIM interface to temporarily unlock the

device.

If desired, the temporary unlock mechanism can be permanently disabled by the user

through OPT6/NOPT6 option bytes.

5.5

Clock controller

The clock controller distributes the system clock coming from different oscillators to the core

and the peripherals. It also manages clock gating for low-power modes and ensures clock

robustness.

5.5.1

Features

•

Clock sources

–

16 MHz high-speed internal RC oscillator (HSI)

–

128 kHz low-speed internal RC (LSI)

–

1-24 MHz high-speed external crystal (HSE)

–

Up to 24 MHz high-speed user-external clock (HSE user-ext)

•

Reset: After reset the microcontroller restarts by default with an internal 2-MHz clock

(16 MHz/8). The clock source and speed can be changed by the application program

as soon as the code execution starts.

•

Safe clock switching: Clock sources can be changed safely on the fly in Run mode

through a configuration register. The clock signal is not switched until the new clock

source is ready. The design guarantees glitch-free switching.

•

Clock management: To reduce power consumption, the clock controller can stop the

clock to the core, individual peripherals or memory.

•

Wakeup: In case the device wakes up from low-power modes, the internal RC

oscillator (16 MHz/8) is used for quick startup. After a stabilization time, the device

switches to the clock source that was selected before Halt mode was entered.

•

Clock security system (CSS): The CSS permits monitoring of external clock sources

and automatic switching to the internal RC (16 MHz/8) in case of a clock failure.

•

Configurable main clock output (CCO): This feature permits to output a clock signal

for use by the application.

5.5.2

16 MHz high-speed internal RC oscillator (HSI)

•

Default clock after reset 2 MHz (16 MHz/8)

•

Fast wakeup time

User trimming

The register CLK_HSITRIMR with two trimming bits plus one additional bit for the sign

permits frequency tuning by the application program. The adjustment range covers all

possible frequency variations versus supply voltage and temperature. This trimming does

not change the initial production setting.

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