AT90SCR100 datasheet(265/433 Pages) ATMEL

265 / 433 page

265

TPR0327AY–SMS–30Jan09

AT90SCR100

• Bit 1 - UCPHA0: Clock Phase

The UCPHA0 bit setting determine if data is sampled on the leasing edge (first) or tailing (last)

edge of XCK0. Refer to the SPI Data Modes and Timing section page 4 for details.

• Bit 0 - UCPOL0: Clock Polarity

The UCPOL0 bit sets the polarity of the XCK0 clock. The combination of the UCPOL0 and

UCPHA0 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

UBRR0L and UBRR0H –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 “UBRR0L and UBRR0H – USART Baud Rate Registers” on page 253.

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 UCPOL0 bit functionality is identical to the SPI CPOL bit.

• The UCPHA0 bit functionality is identical to the SPI CPHA bit.

• The UDORD0 bit functionality is identical to the SPI DORD bit.

However, since the USART in MSPIM mode reuses the USART resources, the use of the

USART in MSPIM mode is somewhat different compared to the SPI. In addition to differences of

the control register bits, and that only master operation is supported by the USART in MSPIM

mode, the following features differ between the two modules:

• The USART in MSPIM mode includes (double) buffering of the transmitter. The SPI has no

buffer.

• The USART in MSPIM mode receiver includes an additional buffer level.

• The SPI WCOL (Write Collision) bit is not included in USART in MSPIM mode.

• The SPI double speed mode (SPI2X) bit is not included. However, the same effect is

achieved by setting UBRR0 accordingly.

• Interrupt timing is not compatible.

• Pin control differs due to the master only operation of the USART in MSPIM mode.

A comparison of the USART in MSPIM mode and the SPI pins is shown in Table 19-4 on page

265.

Table 19-4.

Comparison of USART in MSPIM mode and SPI pins.

USART_MSPIM

SPI

Comment

TxD0

MOSI

Master Out only

RxD0

MISO

Master In only

XCK0

SCK

(Functionally identical)

(N/A)

Not supported by USART in MSPIM

AT90SCR100 Datasheet(PDF) 265 Page - ATMEL Corporation

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