ATMEGA640 datasheet(197/436 Pages) MICROCHIP

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ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

21.2 Register Description

21.2.1

SPCR – SPI Control Register

• 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 if the Global Inter-

rupt Enable bit in SREG is set.

• Bit 6 – SPE: SPI Enable

When the SPE bit is written to 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 written to one, the LSB of the data word is transmitted first.

When the DORD bit is written to zero, the MSB of the data word is transmitted first.

• Bit 4 – MSTR: Master/Slave Select

This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic zero. If SS is config-

ured 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 written to one, SCK is high when idle. When CPOL is written to zero, SCK is low when idle. Refer

to Figure 21-3 on page 196 and Figure 21-4 on page 196 for an example. The CPOL functionality is summarized in

Table 21-3.

• 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 21-3 on page 196 and Figure 21-4 on page 196 for an example. The CPOL functionality is

summarized in Table 21-4.

Bit

765432

0x2C (0x4C)

SPIE

SPE

DORD

MSTR

CPOL

CPHA

SPR1

SPR0

SPCR

Read/Write

R/W

Initial Value

000000

Table 21-3.

CPOL Functionality

CPOL

Leading Edge

Trailing Edge

Rising

Falling

Rising

Table 21-4.

CPHA Functionality

CPHA

Leading Edge

Trailing Edge

Sample

Setup

Sample

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