Datasheet

181
ATmega48PA/88PA/168PA [DATASHEET]
9223F–AVR–04/14
21.8.4 UCSRnC – USART MSPIM Control and Status Register n C
• Bit 7:6 – UMSELn1:0: USART Mode Select
These bits select the mode of operation of the USART as shown in Table 21-4. See Section 20.11.4 “UCSRnC – USART
Control and Status Register n C” on page 173 for full description of the normal USART operation. The MSPIM is enabled
when both UMSELn bits are set to one. The UDORDn, UCPHAn, and UCPOLn can be set in the same write operation where
the MSPIM is enabled.
• Bit 5:3 – Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices, these bits must be written
to zero when UCSRnC is written.
• Bit 2 – UDORDn: Data Order
When set to one the LSB of the data word is transmitted first. When set to zero the MSB of the data word is transmitted first.
Refer to the frame formats section page 4 for details.
• Bit 1 – UCPHAn: Clock Phase
The UCPHAn bit setting determine if data is sampled on the leasing edge (first) or tailing (last) edge of XCKn. Refer to the
SPI data modes and timing section page 4 for details.
• Bit 0 – UCPOLn: Clock Polarity
The UCPOLn bit sets the polarity of the XCKn clock. The combination of the UCPOLn and UCPHAn bit settings determine
the timing of the data transfer. Refer to the SPI data modes and timing section page 4 for details.
21.8.5 USART MSPIM Baud Rate Registers – UBRRnL and UBRRnH
The function and bit description of the baud rate registers in MSPI mode is identical to normal USART operation. See
Section 20.11.5 “UBRRnL and UBRRnH – USART Baud Rate Registers” on page 174.
Bit 7 6 5 4 3 2 1 0
UMSELn1 UMSELn0 – – – UDORDn UCPHAn UCPOLn UCSRnC
Read/Write R/W R/W R R R R/W R/W R/W
Initial Value 0 0 0 0 0 1 1 0
Table 21-4. UMSELn Bits Settings
UMSELn1 UMSELn0 Mode
0 0 Asynchronous USART
0 1 Synchronous USART
1 0 Reserved
1 1 Master SPI (MSPIM)