ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 148

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

148
ATmega325/3250/645/6450
be cleared, and SPIF in SPSR will become set. The user will then have to set MSTR to
re-enable SPI Master mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero,
SCK is low when idle. Refer to Figure 67 and Figure 68 for an example. The CPOL func-
tionality is summarized below:
Table 65. CPOL Functionality
• Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading
(first) or trailing (last) edge of SCK. Refer to Figure 67 and Figure 68 for an example.
The CPOL functionality is summarized below:
Table 66. CPHA Functionality
• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and
SPR0 have no effect on the Slave. The relationship between SCK and the Oscillator
Clock frequency f
Table 67. Relationship Between SCK and the Oscillator Frequency
SPI2X
0
0
0
0
1
1
1
1
CPOL
CPHA
0
1
0
1
osc
is shown in the following table:
SPR1
0
0
1
1
0
0
1
1
Leading Edge
Leading Edge
Sample
Falling
Rising
Setup
SPR0
0
1
0
1
0
1
0
1
SCK Frequency
f
f
f
f
f
f
f
f
osc
osc
osc
osc
osc
osc
osc
osc
/
/
/
/
/
/
/
/
4
16
64
128
2
8
32
64
Trailing Edge
Trailing Edge
Sample
Falling
Rising
Setup
2570A–AVR–09/04