155
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
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
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 fclkio is shown in the following table:
18.5.3
SPSR – SPI Status Register
Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF flag is set. An interrupt is generated if SPIE in SPCR is set and global
interrupts are enabled. If SS is an input and is driven low when the SPI is in Master mode, this will also set the SPIF
flag. SPIF is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, the
SPIF bit is cleared by first reading the SPI Status Register with SPIF set, then accessing the SPI Data Register
(SPDR).
Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The WCOL bit (and the SPIF
bit) are cleared by first reading the SPI Status Register with WCOL set, and then accessing the SPI Data Register.
Bit 5:1 – Res: Reserved
These bits are reserved and will always read as zero.
Table 18-4.
CPHA functionality.
CPHA
Leading edge
Trailing edge
0
Sample
Setup
1
Setup
Sample
Table 18-5.
Relationship between SCK and the oscillator frequency.
SPI2X
SPR1
SPR0
SCK frequency
00
0
f
clkio/4
00
1
f
clkio/16
01
0
f
clkio/64
01
1
f
clkio/128
10
0
f
clkio/2
10
1
f
clkio/8
11
0
f
clkio/32
11
1
f
clkio/64
Bit
76543210
SPIF
WCOL
–
SPI2X
SPSR
Read/write
RRRRRRR
R/W
Initial value
00000000