ATtiny88 datasheet(122/266 Pages) ATMEL

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122

8008C–AVR–03/09

ATtiny48/88

• 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 14-3 and Figure 14-4 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 oscillator clock frequency f

osc is

shown in the following table:

14.5.2

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 Bits

These bits are reserved and will always read zero.

Table 14-4.

CPHA Functionality

CPHA

Leading Edge

Trailing Edge

Sample

Setup

Sample

Table 14-5.

Relationship Between SCK and the Oscillator Frequency

SPI2X

SPR1

SPR0

SCK Frequency

osc/4

osc/16

osc/64

osc/128

osc/2

osc/8

osc/32

osc/64

Bit

654

SPIF

WCOL

–

SPI2X

SPSR

Read/Write

R/W

Initial Value

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