Datasheet

129
ATmega8(L)
2486M–AVR–12/03
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 59 and Figure 60. 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 48 and Table 49, as done below:
Figure 59. SPI Transfer Format with CPHA = 0
Figure 60. SPI Transfer Format with CPHA = 1
Table 51. CPOL and CPHA Functionality
Leading Edge Trailing Edge SPI Mode
CPOL = 0, CPHA = 0 Sample (Rising) Setup (Falling) 0
CPOL = 0, CPHA = 1 Setup (Rising) Sample (Falling) 1
CPOL = 1, CPHA = 0 Sample (Falling) Setup (Rising) 2
CPOL = 1, CPHA = 1 Setup (Falling) Sample (Rising) 3
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
SS
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)
SCK (CPOL = 0)
mode 1
SAMPLE I
MOSI/MISO
CHANGE 0
MOSI PIN
CHANGE 0
MISO PIN
SCK (CPOL = 1)
mode 3
SS
MSB
LSB
Bit 6
Bit 1
Bit 5
Bit 2
Bit 4
Bit 3
Bit 3
Bit 4
Bit 2
Bit 5
Bit 1
Bit 6
LSB
MSB
MSB first (DORD = 0)
LSB first (DORD = 1)