ATMega chip full datasheet - UCSD Department of Physics

ATmega48A/PA/88A/PA/168A/PA/328/P19.5.3 SPDR – SPI Data RegisterBit 7 6 5 4 3 2 1 00x2E (0x4E) MSB LSB SPDRRead/Write R/W R/W R/W R/W R/W R/W R/W R/WInitial Value X X X X X X X X UndefinedThe SPI Data Register is a read/write register used for data transfer between the Register Fileand the SPI Shift Register. Writing to the register initiates data transmission. Reading the registercauses the Shift Register Receive buffer to be read.8271D–AVR–05/11177