MC68HC705P9CS datasheet(120/160 Pages) FREESCALE

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Serial Input/Output Port (SIOP)

Technical Data

MC68HC705P9 — Rev. 4.0

120

Serial Input/Output Port (SIOP)

MOTOROLA

10.4 Operation

The master MCU initiates and controls the transfer of data to and from

one or more slave peripheral devices. In master mode, a transmission is

initiated by writing to the SIOP data register (SDR). Data written to the

SDR is parallel-loaded and shifted out serially to the slave device(s).

Many simple slave devices are designed to only receive data from a

master or to only supply data to a master. For example, when a serial-

to-parallel shift register is used as an 8-bit port, the master MCU initiates

transfers of 8-bit data values to the shift register. Since the serial-to-

parallel shift register does not send any data to the master, the MCU

ignores whatever it receives as a result of the transmission.

The SIOP is simpler than the serial peripheral interface (SPI) on some

other Motorola MCUs in that:

•

The polarity of the serial clock is fixed.

•

There is no slave select pin.

•

The direction of serial data does not automatically switch as on the

SPI because the SIOP is not intended for use in multimaster

systems. Most applications use one MCU as the master to initiate

and control data transfer between one or more slave peripheral

devices.

A programmable option allows the SIOP to transfer data MSB first or

LSB first.

10.4.1 Pin Functions

The SIOP uses three pins and shares them with port B:

•

PB7/SCK

•

PB6/SDI

•

PB5/SDO

NOTE:

Do not use the PB7/SCK, PB6/SDI, or PB5/SDO pins for general-

purpose I/O while the SIOP is enabled.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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