Datasheet

244
ATmega640/1280/1281/2560/2561
2549K–AVR–01/07
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 115. See
“UCSRnC – USART Control and Status Register n C” on page 229 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.
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 USART operation. See “UBRRnL and UBRRnH – USART Baud Rate Registers”
on page 231.
Bit 7 6 5 4 3 2 1 0
UMSELn1 UMSELn0 - - - UDORDn UCPHAn UCPOLn UCSRnC
Read/Write R/W R/W RRR R/W R/W R/W
Initial Value 0 0 0 0 0 1 1 0
Table 115. UMSELn Bits Settings
UMSELn1 UMSELn0 Mode
0 0 Asynchronous USART
0 1 Synchronous USART
1 0 (Reserved)
1 1 Master SPI (MSPIM)
Table 116. Comparison of USART in MSPIM mode and SPI pins.
USART_MSPIM SPI Comment
TxDn MOSI Master Out only
RxDn MISO Master In only
XCKn SCK (Functionally identical)
(N/A) SS
Not supported by USART in MSPIM