AT90USB82/162
18.6.4
USART MSPIM Control and Status Register n C - UCSRnC
Bit
7
6
5
-
4
-
3
-
2
1
0
UMSELn1
UMSELn0
UDORDn
UCPHAn
UCPOLn
UCSRnC
Read/Write
Initial Value
R/W
0
R/W
0
R
0
R
0
R
0
R/W
1
R/W
1
R/W
0
• Bit 7:6 - UMSELn1:0: USART Mode Select
These bits select the mode of operation of the USART as shown in Table 18-3. See “USART
Control and Status Register n C – UCSRnC” on page 167 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.
Table 18-3. UMSELn Bits Settings
UMSELn1
UMSELn0
Mode
0
0
1
1
0
Asynchronous USART
Synchronous USART
(Reserved)
1
0
1
Master SPI (MSPIM)
• 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.
18.6.5
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 “USART Baud Rate Registers – UBRRLn and UBRRHn” on page 169.
18.7 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.
181
7707D–AVR–07/08
ATMEL [ ATMEL ]
