Atmel ATmega48A Manual page 247

ATmega48A/PA/88A/PA/168A/PA/328/P
Figure 22-22. TWI Address Match Logic, Block Diagram
TWAR0
Address
Match
Address
Bit 0
TWAMR0
Address Bit Comparator 0
Address Bit Comparator 6..1
• Bit 0 – Reserved
This bit is an unused bit in the ATmega48A/PA/88A/PA/168A/PA/328/P, and will always read as
zero.
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