ST92141 datasheet(145/179 Pages) STMICROELECTRONICS

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ST92141 - SERIAL PERIPHERAL INTERFACE (SPI)

SERIAL PERIPHERAL INTERFACE (Cont’d)

7.5.6 Register Description

DATA REGISTER (SPDR)

R240 - Read/Write

Reset Value: 0000 0000 (00h)

The DR register is used to transmit and receive

data on the serial bus. In the master device only a

write to this register will initiate transmission/re-

ception of another byte.

Notes: During the last clock cycle the SPIF bit is

set, a copy of the received data byte in the shift

the serial peripheral data register, the buffer is ac-

tually being read.

Warning: A write to the DR register places data di-

rectly into the shift register for transmission.

A read to the DR register returns the value located

in the buffer and not the content of the shift regis-

ter (see Figure 73).

CONTROL REGISTER (SPCR)

R241 - Read/Write

Reset Value: 0000 0000 (00h)

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 either

SPIF or MODF are set in the SR register while

the other flag is 0.

Bit 6 = SPOE

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 7.5.4.5 Master Mode Fault).

0: SPI alternate functions disabled (MISO, MOSI

and SCK can only work as input)

1: SPI alternate functions enabled (MISO, MOSI

and SCK can work as input or output depending

on the value of MSTR)

Note: To use the MISO, MOSI and SCK alternate

functions (input or output), the corresponding I/O

port must be programmed as alternate function

output.

Bit 5 = SPIS

Interrupt Selection.

This bit is set and cleared by software.

0: Interrupt source is external interrupt

1: Interrupt source is SPI

Bit 4 = MSTR

Master.

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

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

(see Section 7.5.4.5 Master Mode Fault).

0: Slave mode is selected

1: Master mode is selected, the function of the

SCK pin changes from an input to an output and

the functions of the MISO and MOSI pins are re-

versed.

Bit 3 = CPOL

Clock polarity.

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

termines the steady state of the serial Clock. The

CPOL bit affects both the master and slave

modes.

0: The steady state is a low value at the SCK pin.

1: The steady state is a high value at the SCK pin.

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.

Bit 1:0 = SPR[1:0]

Serial peripheral rate.

These bits are set and cleared by software. They

select one of four baud rates to be used as the se-

rial clock when the device is a master.

These 2 bits have no effect in slave mode.

Table 28. Serial Peripheral Baud Rate

SPIE

SPOE SPIS MSTR

CPOL

CPHA

SPR1

SPR0

INTCLK Clock Divide

SPR1

SPR0

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