3 data mode, Atmega128rfa1 – Rainbow Electronics ATmega128RFA1 User Manual

Page 335

335

8266A-MCU Wireless-12/09

ATmega128RFA1

22.3.3 Data Mode

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 22-3 below

and

Figure 22-4 below

. Data bits are shifted out and

latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals
to stabilize. This is clearly seen in the summary of

Table 22-2 below

Table 22-2. 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)

Figure 22-3. SPI Transfer Format with CPHA = 0

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 3
Bit 4

Bit 2
Bit 5

MSB first (DORD = 0)
LSB first (DORD = 1)

Figure 22-4. SPI Transfer Format with CPHA = 1

SCK (CPOL = 0)
mode 1