DSP56364 datasheet(11/148 Pages) FREESCALE

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Serial Host Interface

DSP56364 Technical Data, Rev. 4.1

Freescale Semiconductor

2-7

2.7

Serial Host Interface

The SHI has five I/O signals that can be configured to allow the SHI to operate in either SPI or I2C mode.

Table 2-9 Serial Host Interface Signals

Signal

Name

Signal

Type

State During

Reset

Signal Description

SCK

Input or

output

Tri-stated

SPI Serial Clock—The SCK signal is an output when the SPI is configured as a master

and a Schmitt-trigger input when the SPI is configured as a slave. When the SPI is

configured as a master, the SCK signal is derived from the internal SHI clock generator.

When the SPI is configured as a slave, the SCK signal is an input, and the clock signal

from the external master synchronizes the data transfer. The SCK signal is ignored by

the SPI if it is defined as a slave and the slave select (SS) signal is not asserted. In both

the master and slave SPI devices, data is shifted on one edge of the SCK signal and is

sampled on the opposite edge where data is stable. Edge polarity is determined by the

SPI transfer protocol.

SCL

Input or

output

Tri-stated

I2C Serial Clock—SCL carries the clock for I2C bus transactions in the I2C mode. SCL

is a Schmitt-trigger input when configured as a slave and an open-drain output when

configured as a master. SCL should be connected to VCC through a pull-up resistor.

This signal is tri-stated during hardware, software, and individual reset. Thus, there is

no need for an external pull-up in this state.

This input is 5 V tolerant.

MISO

Input or

output

Tri-stated

SPI Master-In-Slave-Out—When the SPI is configured as a master, MISO is the

master data input line. The MISO signal is used in conjunction with the MOSI signal for

transmitting and receiving serial data. This signal is a Schmitt-trigger input when

configured for the SPI Master mode, an output when configured for the SPI Slave

mode, and tri-stated if configured for the SPI Slave mode when SS is deasserted. An

external pull-up resistor is not required for SPI operation.

SDA

Input or

open-drain

output

Tri-stated

I2C Data and Acknowledge—In I2C mode, SDA is a Schmitt-trigger input when

receiving and an open-drain output when transmitting. SDA should be connected to

VCC through a pull-up resistor. SDA carries the data for I

2C transactions. The data in

SDA must be stable during the high period of SCL. The data in SDA is only allowed to

change when SCL is low. When the bus is free, SDA is high. The SDA line is only

allowed to change during the time SCL is high in the case of start and stop events. A

high-to-low transition of the SDA line while SCL is high is a unique situation, and is

defined as the start event. A low-to-high transition of SDA while SCL is high is a unique

situation defined as the stop event.

This signal is tri-stated during hardware, software, and individual reset. Thus, there is

no need for an external pull-up in this state.

This input is 5 V tolerant.

MOSI

Input or

output

Tri-stated

SPI Master-Out-Slave-In—When the SPI is configured as a master, MOSI is the

master data output line. The MOSI signal is used in conjunction with the MISO signal

for transmitting and receiving serial data. MOSI is the slave data input line when the

SPI is configured as a slave. This signal is a Schmitt-trigger input when configured for

the SPI Slave mode.

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