183
7799D–AVR–11/10
ATmega8U2/16U2/32U2
19.7.4
UCSRnC – USART MSPIM Control and Status Register n C
Bit 7:6 - UMSELn[1:0]: USART Mode Select
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.
19.7.5
UBRRnL and UBRRnH – USART MSPIM Baud Rate Registers
The function and bit description of the baud rate registers in MSPI mode is identical to normal
19.8
AVR USART MSPIM vs. AVR SPI
The USART in MSPIM mode is fully compatible with the AVR SPI regarding:
Master mode timing diagram.
The UCPOLn bit functionality is identical to the SPI CPOL bit.
The UCPHAn bit functionality is identical to the SPI CPHA bit.
The UDORDn bit functionality is identical to the SPI DORD bit.
Bit
7
6
5
4
3
2
1
0
UMSELn1
UMSELn0
–
UDORDn
UCPHAn
UCPOLn
UCSRnC
Read/Write
R/W
R
R/W
Initial Value
0
1
0
Table 19-3.
UMSELn Bits Settings
UMSELn1
UMSELn0
Mode
0
Asynchronous USART
0
1
Synchronous USART
1
0
(Reserved)
1
Master SPI (MSPIM)