ATMEGA649 datasheet(160/375 Pages) ATMEL

160 / 375 page

160

ATmega329/339/649/659

2552H–AVR–11/06

Data Modes

There are four combinations of SCK phase and polarity with respect to serial data,

which are determined by control bits CPHA and CPOL. The SPI data transfer formats

are shown in Figure 68 and Figure 69. Data bits are shifted out and latched in on oppo-

site edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is

clearly seen by summarizing Table 73 and Table 74, as done below:

Figure 68. SPI Transfer Format with CPHA = 0

Figure 69. SPI Transfer Format with CPHA = 1

Table 76. CPOL Functionality

Leading Edge

Trailing eDge

SPI Mode

CPOL=0, CPHA=0

Sample (Rising)

Setup (Falling)

CPOL=0, CPHA=1

Setup (Rising)

Sample (Falling)

CPOL=1, CPHA=0

Sample (Falling)

Setup (Rising)

CPOL=1, CPHA=1

Setup (Falling)

Sample (Rising)

Bit 1

Bit 6

LSB

MSB

SCK (CPOL = 0)

mode 0

SAMPLE I

MOSI/MISO

CHANGE 0

MOSI PIN

CHANGE 0

MISO PIN

SCK (CPOL = 1)

mode 2

MSB

LSB

Bit 6

Bit 1

Bit 5

Bit 2

Bit 4

Bit 3

Bit 4

Bit 2

Bit 5

MSB first (DORD = 0)

LSB first (DORD = 1)

SCK (CPOL = 0)

mode 1

SAMPLE I

MOSI/MISO

CHANGE 0

MOSI PIN

CHANGE 0

MISO PIN

SCK (CPOL = 1)

mode 3

MSB

LSB

Bit 6

Bit 1

Bit 5

Bit 2

Bit 4

Bit 3

Bit 4

Bit 2

Bit 5

Bit 1

Bit 6

LSB

MSB

MSB first (DORD = 0)

LSB first (DORD = 1)

ATMEGA649 Datasheet(PDF) 160 Page - ATMEL Corporation

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