Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet

Product codes
MEGA328P-XMINI
Page of 657
642
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
40.6.1 Rev E
Analog MUX can be turned off when setting ACME bit
TWI Data setup time can be too short
1.
Analog MUX can be turned off when setting ACME bit
If the ACME (Analog Comparator Multiplexer Enabled) bit in ADCSRB is set while MUX3 in ADMUX is '1' 
(ADMUX[3:0]=1xxx), all MUXes are turned off until the ACME bit is cleared.
Problem Fix/Workaround
Clear the MUX3 bit before setting the ACME bit.
2.
TWI Data setup time can be too short
When running the device as a TWI slave with a system clock above 2MHz, the data setup time for the first 
bit after ACK may in some cases be too short. This may cause a false start or stop condition on the TWI 
line.
Problem Fix/Workaround
Insert a delay between setting TWDR and TWCR.