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Motorola DSP56012 User Manual

Page 54

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2-14

DSP56012 User’s Manual

MOTOROLA

Signal Descriptions

Serial Host Interface (SHI)

MISO/
SDA

Input or
Output

Tri-stated

SPI Master-In-Slave-Out/I

2

C Data and

Acknowledge

—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.

In I

2

C mode, SDA is a Schmitt-trigger input when receiving

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

CC

through a pull-up resistor. SDA carries the

data for I

2

C 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 an
unique situation, which is defined as the start event. A low to
high transition of SDA while SCL is high is an unique
situation, which is defined as the stop event.

An external pull-up resistor is not required.

MOSI/
HA0

Input or
Output

Tri-stated

SPI Master-Out-Slave-In/I2C Slave Address 0

—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.

This signal uses a Schmitt-trigger input when configured for
the I

2

C mode. When configured for I

2

C Slave mode, the HA0

signal is used to form the slave device address. HA0 is
ignored when it is configured for the I

2

C Master mode.

An external pull-up resistor is not required.

Table 2-7

Serial Host Interface (SHI) Signals (Continued)

Signal

Name

Signal

Type

State

during

Reset

Signal Description