Motorola DSP56012 User Manual

MISO/ 
SDA

Input or 
Output

Tri-stated

—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

—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.

Serial Host Interface (SHI) Signals  (Continued)