174
7679H–CAN–08/08
AT90CAN32/64/128
and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable SPI Mas-
ter 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
and
for an example. The CPOL functionality is sum-
marized below:
• 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
for an example. The CPOL
functionality is summarized below:
• 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 clk
IO
frequency f
clkio
is shown in
the following table:
Table 16-2.
CPOL Functionality
CPOL
Leading Edge
Trailing Edge
0
Rising
Falling
1
Falling
Rising
Table 16-3.
CPHA Functionality
CPHA
Leading Edge
Trailing Edge
0
Sample
Setup
1
Setup
Sample
Table 16-4.
Relationship Between SCK and the Oscillator Frequency
SPI2X
SPR1
SPR0
SCK Frequency
0
0
0
f
clkio
/
4
0
0
1
f
clkio
/
16
0
1
0
f
clkio
/
64
0
1
1
f
clkio
/
128
1
0
0
f
clkio
/
2
1
0
1
f
clkio
/
8
1
1
0
f
clkio
/
32
1
1
1
f
clkio
/
64