DSP56362P datasheet(20/152 Pages) FREESCALE

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Serial Host Interface

DSP56362 Technical Data, Rev. 4

2-14

Freescale Semiconductor

2.8

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 2-10 Serial Host Interface Signals

Signal Name

Signal Type

State during

Reset

Signal Description

SCK

SCL

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.

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

SDA

Input or Output

Input or Open-Drain

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.

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 I2C 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.

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