AT89C51ED2-RDTIM datasheet(66/137 Pages) ATMEL

66 / 137 page

AT89C51RD2/ED2

4235E–8051–04/04

Functional Description

Figure 30 shows a detailed structure of the SPI Module.

Figure 30. SPI Module Block Diagram

Operating Modes

The Serial Peripheral Interface can be configured in one of the two modes: Master mode

or Slave mode. The configuration and initialization of the SPI Module is made through

one register:

•

The Serial Peripheral Control register (SPCON)

Once the SPI is configured, the data exchange is made using:

•SPCON

•

The Serial Peripheral STAtus register (SPSTA)

•

The Serial Peripheral DATa register (SPDAT)

During an SPI transmission, data is simultaneously transmitted (shifted out serially) and

received (shifted in serially). A serial clock line (SCK) synchronizes shifting and sam-

pling on the two serial data lines (MOSI and MISO). A Slave Select line (SS) allows

individual selection of a Slave SPI device; Slave devices that are not selected do not

interfere with SPI bus activities.

When the Master device transmits data to the Slave device via the MOSI line, the Slave

device responds by sending data to the Master device via the MISO line. This implies

full-duplex transmission with both data out and data in synchronized with the same clock

(Figure 31).

Shift Register

Internal Bus

Control

Logic

MISO

MOSI

SCK

Clock

Logic

Clock

Divider

Clock

Select

/64

/128

SPI Interrupt Request

8-bit bus

1-bit signal

FCLK PERIPH

/32

/16

Receive Data Register

SPDAT

SPI

Control

SPSTA

CPHA

SPR0

SPR1

CPOL

MSTR

SSDIS

SPEN

SPR2

SPCON

WCOL

MODF

SPIF

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