Datasheet

24.8.4. TWDR – TWI Data Register
When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When
addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these offset
addresses.
In Transmit mode, TWDR contains the next byte to be transmitted. In Receive mode, the TWDR contains
the last byte received. It is writable while the TWI is not in the process of shifting a byte. This occurs when
the TWI Interrupt Flag (TWINT) is set by hardware. Note that the Data Register cannot be initialized by
the user before the first interrupt occurs. The data in TWDR remains stable as long as TWINT is set.
While data is shifted out, data on the bus is simultaneously shifted in. TWDR always contains the last
byte present on the bus, except after a wake up from a sleep mode by the TWI interrupt. In this case, the
contents of TWDR is undefined. In the case of a lost bus arbitration, no data is lost in the transition from
Master to Slave. Handling of the ACK bit is controlled automatically by the TWI logic, the CPU cannot
access the ACK bit directly.
Name: TWDR
Offset: 0x03
Reset: 0xFF
Property: When addressing I/O Registers as data space the offset address is 0x23
Bit 7 6 5 4 3 2 1 0
TWD7 TWD6 TWD5 TWD4 TWD3 TWD2 TWD1 TWD0
Access
R/W R/W R/W R/W R/W R/W R/W R/W
Reset 0 0 0 0 0 0 0 1
Bits 7:0 – TWDn: TWI Data [n = 7:0]
These eight bits constitute the next data byte to be transmitted, or the latest data byte received on the 2-
wire Serial Bus.
Atmel ATmega32A [DATASHEET]
Atmel-8155I-ATmega32A_Datasheet_Complete-08/2016
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