Motorola DSP56012 - Manual (Page 54)

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