Datasheet

309
7734Q–AVR–02/12
AT90PWM81/161
1. Clock Switch enable & disable
After a “Enable Clock Source” or a “Disable Clock Source” command, the command is still
active until the next access of CLKCSR register. If CLKSEL is written with a new value, the
corresponding clock will be unintentionnaly enabled or disabled.
Work around:
Atter the Enable or Disable command, write CLKCSR with value 1<<CLKCCE
2. Crystal oscillator control with Clock Switch
When a Xtal oscillator is active and CLKSELR is written with a new value for the selection of
another clock source (for instance RC or WD) , the Xtal oscillator gain is not correct.
Work around:
After the commands “Enable Clock Source” and “Clock Source Switching”, write back CLK-
SELR with the values corresponding to the active Xtal oscillator
3. BOD disable fuse
It is strongly advised to keep the BOD active. Indeed, the RC oscillator may lock if it is acti-
vated when the power suppy goes at a low voltage.
Work around:
If it is mandatory to disable the BOD, do not set the RC oscillator as clock source during
reset and makes sure the RC oscillator is never active when the power supply is below the
lowest POR voltage (2.6V).
4. PSC output at Reset
At Reset, the PSC outputs may be set at a value different from the PSC Fuse configuration
(Bit 4 of Extended Fuse Byte).
Work around:
Initiate PSC output states from source code.
5. Flash and EEPROM programming failure if CPU clock is switched
If Clock switching is used in the Application, the memory programming is only possible when
the internal RC oscillator is selected as System clock.
If the Application requires a memory programming on a clock source different from the inter-
nal RC oscillator, do not switch to this clock source.
Work around:
- Use internal RC oscillator when programming Flash and EEPROM,
or
- Do not use clock switching
6. ADC AMPlifier measurement is unstable
When switching from a single-ended ADC channel to an Amplified channel, noise can
appear on ADC conversion.
Work around:
After switching from a single ended to an amplified channel, discard the first ADC
conversion.