
1-10
DSP56007/D MOTOROLA
Signal/Connection Descriptions
Serial Host Interface (SHI)
SERIAL HOST INTERFACE (SHI)
The Serial Host Interface
(SHI) has five I/O signals, which may be configured to
operate in either SPI or I
2
lists the SHI signals.
Table 1-8
Serial Host Interface (SHI) signals
Signal Name
Signal
Type
State
during
Reset
Signal Description
SCK
SCL
Input or
Output
Input or
Output
Tri-stated
SPI Serial Clock (SCK)
—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.
I
2
C Serial Clock (SCL)
—SCL carries the clock for bus
transactions in the I
2
C 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 V
CC
through a pull-up resistor. The
maximum allowed internally generated bit clock
frequency is
F
osc
/
4
for the SPI mode and
F
osc
/
6
for the
I
2
C mode where F
osc
is the clock on EXTAL. The
maximum allowed externally generated bit clock
frequency is
F
osc
/
3
for the SPI mode and
F
osc
/
5
for the
I
2
C mode. This signal is tri-stated during hardware reset,
software reset, or individual reset (no need for external
pull-up in this state).
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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