ATMEGA640 datasheet(235/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

23.6.4

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 23-3. See “UCSRnC – USART Control

and Status Register n C” on page 221 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 oper-

ation 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 trans-

mitted first. Refer to “SPI Data Modes and Timing” on page 228 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 “SPI Data Modes and Timing” on page 228 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 “SPI Data Modes and Timing” on page 228 for details.

23.6.5

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 USART operation.

See “UBRRnL and UBRRnH – USART Baud Rate Registers” on page 222.

Bit

76543210

UMSELn1

UMSELn0

UDORDn

UCPHAn

UCPOLn

UCSRnC

Read/Write

R/W

Initial Value

00000110

Table 23-3.

UMSELn Bits Settings

UMSELn1

UMSELn0

Mode

Asynchronous USART

Synchronous USART

(Reserved)

Master SPI (MSPIM)

Table 23-4.

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)

Not supported by USART in MSPIM

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