DocID027290 Rev 1

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AN4635

Power consumption comparison

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6.6

Changing AHB divider ratio

Changing the AHB divider ratio leads to decreased power consumption since most of the

circuitry runs at lower frequency.

This is demonstrated in Figure 7, where the black line is the current absorption of the

example running at 1 MHz MSI clock, and the red line is the same code running with AHB

divider set to 4. If the clock can be directly configured to lower frequency, it is always better

to choose this option. The green line represents the same example, only the MSI oscillator

is set directly to 250 kHz. Proven by the difference between Sleep mode and run phase the

actual processing power is the same, but the solution without AHB divider is more efficient.

Use of the AHB divider only makes sense with external clock or if there is necessity to use

the HSI.

Figure 7. Lowering oscillator speed compared to AHB divider

Baud rate

9600

SW used

Blocking operation (Com Polling) with RXSLEEP and TXSLEEP defined

Table 8. Configurations - Core clock speed (continued)

Black

Green

Red