Serial Host Interface - Motorola DSP56367 User Manual

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
2
I C mode.
Signal
Signal Type
Name
SCK Input or
output
SCL Input or
output
MISO Input or
output
SDA Input or
open-drain
output
MOTOROLA
Table 2-10 Serial Host Interface Signals
State
during
Reset
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.
2
I C Serial Clock—SCL carries the clock for I
Schmitt-trigger input when configured as a slave and an open-drain output when configured
as a master. SCL should be connected to V
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 3.3V tolerant.
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.
2
I C Data and Acknowledge—In I
and an open-drain output when transmitting. SDA should be connected to V
pull-up resistor. SDA carries the data for I
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 3.3V tolerant.
DSP56367
Signal/Connection Descriptions
Serial Host Interface
Signal Description
2
C bus transactions in the I
through a pull-up resistor.
CC
2
C mode, SDA is a Schmitt-trigger input when receiving
2
C transactions. The data in SDA must be stable
2
C mode. SCL is a
through a
CC
2-13