ST72260G datasheet(82/171 Pages) STMICROELECTRONICS

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SERIAL PERIPHERAL INTERFACE (Cont’d)

11.4.8 Register Description

CONTROL REGISTER (SPICR)

Read/Write

Reset Value: 0000 xxxx (0xh)

Bit 7 = SPIE

Serial Peripheral Interrupt Enable.

This bit is set and cleared by software.

0: Interrupt is inhibited

1: An SPI interrupt is generated whenever an End

of Transfer event, Master Mode Fault or Over-

run error occurs (SPIF=1, MODF=1 or OVR=1

in the SPICSR register)

Bit 6 = SPE

Serial Peripheral Output Enable.

This bit is set and cleared by software. It is also

cleared by hardware when, in master mode, SS=0

(see

Section

11.4.5.1

"Master

Mode

Fault

(MODF)" on page 79). The SPE bit is cleared by

reset, so the SPI peripheral is not initially connect-

ed to the external pins.

0: I/O pins free for general purpose I/O

1: SPI I/O pin alternate functions enabled

Bit 5 = SPR2

Divider Enable.

This bit is set and cleared by software and is

cleared by reset. It is used with the SPR[1:0] bits to

set the baud rate. Refer to Table 16 SPI Master

mode SCK Frequency.

0: Divider by 2 enabled

1: Divider by 2 disabled

Note: This bit has no effect in slave mode.

Bit 4 = MSTR

Master Mode.

This bit is set and cleared by software. It is also

cleared by hardware when, in master mode, SS=0

(see

Section

11.4.5.1

"Master

Mode

Fault

(MODF)" on page 79).

0: Slave mode

1: Master mode. The function of the SCK pin

changes from an input to an output and the func-

tions of the MISO and MOSI pins are reversed.

Bit 3 = CPOL

Clock Polarity.

This bit is set and cleared by software. This bit de-

termines the idle state of the serial Clock. The

CPOL bit affects both the master and slave

modes.

0: SCK pin has a low level idle state

1: SCK pin has a high level idle state

Note: If CPOL is changed at the communication

byte boundaries, the SPI must be disabled by re-

setting the SPE bit.

Bit 2 = CPHA

Clock Phase.

This bit is set and cleared by software.

0: The first clock transition is the first data capture

edge.

1: The second clock transition is the first capture

edge.

Note: The slave must have the same CPOL and

CPHA settings as the master.

Bits 1:0 = SPR[1:0]

Serial Clock Frequency.

These bits are set and cleared by software. Used

with the SPR2 bit, they select the baud rate of the

SPI serial clock SCK output by the SPI in master

mode.

Note: These 2 bits have no effect in slave mode.

Table 16. SPI Master mode SCK Frequency

SPIE

SPE

SPR2

MSTR

CPOL

CPHA

SPR1

SPR0

Serial Clock

SPR2

SPR1

SPR0

fCPU/4

fCPU/8

fCPU/16

fCPU/32

fCPU/64

fCPU/128

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