Rainbow Electronics ATmega32L - Manual (Page 137)

137
ATmega32(L)
2503C–AVR–10/02
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 67 and Figure 68. 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 56 and Table 57, as done below:
Figure 67. SPI Transfer Format with CPHA = 0
Figure 68. SPI Transfer Format with CPHA = 1
Table 59. 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)