AT43USB355 datasheet(57/115 Pages) ATMEL

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AT43USB355

2603G–USB–04/06

SPI Control Register – SPCR

•Bit 7 – SPIE: SPI Interrupt Enable

This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR register is set and the

global interrupts are enabled.

•Bit 6 – SPE: SPI Enable

When the SPE bit is set (one), the SPI is enabled. This bit must be set to enable any SPI

operations.

•Bit 5 – DORD: Data Order

When the DORD bit is set (one), the LSB of the data word is transmitted first.

When the DORD bit is cleared (zero), the MSB of the data word is transmitted first.

•Bit 4 – MSTR: Master/Slave Select

This bit selects Master SPI mode when set (one), and Slave SPI mode when cleared (zero). If

SS is configured as an input and is driven low while MSTR is set, MSTR will 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 set (one), SCK is high when idle. When CPOL is cleared (zero), SCK is low

when idle. Refer to Figure 20 and Figure 21 for additional information.

•Bit 2 – CPHA: Clock Phase

Refer to Figure 20 or Figure 21 for the functionality of this bit.

• 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

CL is shown in the following table:

Bit

$0D ($2D)

SPIE

SPE

DORD

MSTR

CPOL

CPHA

SPR1

SPR0

SPCR

Read/Write

R/W

Initial Value

Table 20. Relationship Between SCK and the Oscillator Frequency

SPR1

SPR0

SCK Frequency

3 MHz

750 kHz

187.5 kHz

93.75 kHz

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